Fixing FlowJS typing

There's probably still an issue with react-timeago not being properly
ignored yet.

See #2350

assets/js/actions/survey.js

@@ -369,7 +369,7 @@ export const deleteLink = (link: Link) => ({
   link,
 })
 
-export const generatingFile = (file: String) => ({
+export const generatingFile = (file: string) => ({
   type: GENERATING_FILE,
   file
 })

assets/js/components/respondents/RespondentIndex.jsx

@@ -56,10 +56,11 @@ type Props = {
   q: string,
   fields: Array<Object>,
   selectedFields: Array<string>,
+  respondentsFiles: { files: SurveyFiles },
 }
 
 type State = {
-  shownFile: string,
+  shownFile: ?string,
   filesFetchTimer: ?IntervalID,
 }
 
@@ -485,7 +486,7 @@ class RespondentIndex extends Component<Props, State> {
 
       const downloadButtonClass = fileExists ? "black-text" : "grey-text"
       const downloadButtonOnClick = fileExists ? item.onDownload : null
-      const createdAtLabel = fileExists ? <TimeAgo date={fileStatus.created_at * 1000} formatter={this.timeFormatter} /> : null
+      const createdAtLabel = fileExists ? <TimeAgo date={(fileStatus?.created_at || 0) * 1000} formatter={this.timeFormatter} /> : null
 
       const fileCreating = !!fileStatus?.creating
       const generateButtonClass = fileCreating ? "btn-icon-grey" : "black-text"

assets/js/decls/survey.js

@@ -148,7 +148,7 @@ export type Response = {
 export type Disposition = null | "completed" | "partial" | "ineligible"
 
 export type FileStatus = {
-  created_at: Date?,
+  created_at: ?Date,
   creating: boolean,
   file_type: string,
 }