fix doc test

martian/src/stage.rs

@@ -217,7 +217,7 @@ impl Resource {
     /// ```rust
     /// use martian::Resource;
     ///
-    /// let resource = Resource::new().mem_gb(2).vmem_gb(4).special(1, 8);
+    /// let resource = Resource::new().mem_gb(2).vmem_gb(4).special("gpu_count1_mem8".to_owned());
     /// assert_eq!(resource.get_mem_gb(), Some(2));
     /// assert_eq!(resource.get_vmem_gb(), Some(4));
     /// assert_eq!(resource.get_threads(), None);