Add button role to select trigger (#309)

This results in a few a11y improvements:
* Screen readers will better announce the menu button as actionable
* Screen reader focus is correctly returned back to the menu button -- Select was
  already returning focus to the menu button programatically, but
  because the menu button only had tabindex it wasn't seen by screen
  readers as an interactive element. Screen reader focus would be stuck
  on the selected menu item instead of being returned to the button.

src/components/Forms/Select.js

@@ -269,6 +269,9 @@ class Select extends React.PureComponent {
       <div
         onFocus={this.handleFocus}
         onBlur={this.handleBlur}
+        tabIndex={0}
+        role="button"
+        ref={ (node) => this.trigger = node }
       >
         <div
           style={[
@@ -279,8 +282,6 @@ class Select extends React.PureComponent {
           ]}
           aria-required={required}
           aria-invalid={hasError}
-          tabIndex={0}
-          ref={ (node) => this.trigger = node }
         >
           <FloatingLabel
             text={floatingLabelText}

src/components/Forms/__tests__/__snapshots__/Select.spec.js.snap

@@ -46,6 +46,8 @@ exports[`renders Select correctly 1`] = `
               onBlur={[Function]}
               onFocus={[Function]}
               onMouseDown={[Function]}
+              role="button"
+              tabIndex={0}
             >
               <div
                 aria-invalid={false}
@@ -76,7 +78,6 @@ exports[`renders Select correctly 1`] = `
                     "position": "relative",
                   }
                 }
-                tabIndex={0}
               >
                 <label
                   data-radium={true}
@@ -422,6 +423,8 @@ exports[`renders Select w/ server error correctly 1`] = `
               onBlur={[Function]}
               onFocus={[Function]}
               onMouseDown={[Function]}
+              role="button"
+              tabIndex={0}
             >
               <div
                 aria-invalid={false}
@@ -452,7 +455,6 @@ exports[`renders Select w/ server error correctly 1`] = `
                     "position": "relative",
                   }
                 }
-                tabIndex={0}
               >
                 <label
                   data-radium={true}
@@ -800,6 +802,8 @@ exports[`renders disabled Select correctly 1`] = `
               onBlur={[Function]}
               onFocus={[Function]}
               onMouseDown={[Function]}
+              role="button"
+              tabIndex={0}
             >
               <div
                 aria-invalid={false}
@@ -830,7 +834,6 @@ exports[`renders disabled Select correctly 1`] = `
                     "position": "relative",
                   }
                 }
-                tabIndex={0}
               >
                 <label
                   data-radium={true}
@@ -1176,6 +1179,8 @@ exports[`renders invalid Select correctly 1`] = `
               onBlur={[Function]}
               onFocus={[Function]}
               onMouseDown={[Function]}
+              role="button"
+              tabIndex={0}
             >
               <div
                 aria-invalid={false}
@@ -1206,7 +1211,6 @@ exports[`renders invalid Select correctly 1`] = `
                     "position": "relative",
                   }
                 }
-                tabIndex={0}
               >
                 <label
                   data-radium={true}
@@ -1551,6 +1555,8 @@ exports[`uses a custom theme for all child components if one is provided 1`] = `
             onBlur={[Function]}
             onFocus={[Function]}
             onMouseDown={[Function]}
+            role="button"
+            tabIndex={0}
           >
             <div
               aria-invalid={false}
@@ -1581,7 +1587,6 @@ exports[`uses a custom theme for all child components if one is provided 1`] = `
                   "position": "relative",
                 }
               }
-              tabIndex={0}
             >
               <label
                 data-radium={true}