prettier: convert app/js decaffeinated files to Prettier format

app/js/ContentTypeMapper.js

@@ -3,31 +3,36 @@
 */
 // TODO: This file was created by bulk-decaffeinate.
 // Fix any style issues and re-enable lint.
-let ContentTypeMapper;
-const Path = require('path');
+let ContentTypeMapper
+const Path = require('path')
 
 // here we coerce html, css and js to text/plain,
 // otherwise choose correct mime type based on file extension,
 // falling back to octet-stream
-module.exports = (ContentTypeMapper = {
-	map(path) {
-		switch (Path.extname(path)) {
-			case '.txt': case '.html': case '.js': case '.css': case '.svg':
-				return 'text/plain';
-			case '.csv':
-				return 'text/csv';
-			case '.pdf':
-				return 'application/pdf';
-			case '.png':
-				return 'image/png';
-			case '.jpg': case '.jpeg':
-				return 'image/jpeg';
-			case '.tiff':
-				return 'image/tiff';
-			case '.gif':
-				return 'image/gif';
-			default:
-				return 'application/octet-stream';
-		}
-	}
-});
+module.exports = ContentTypeMapper = {
+  map(path) {
+    switch (Path.extname(path)) {
+      case '.txt':
+      case '.html':
+      case '.js':
+      case '.css':
+      case '.svg':
+        return 'text/plain'
+      case '.csv':
+        return 'text/csv'
+      case '.pdf':
+        return 'application/pdf'
+      case '.png':
+        return 'image/png'
+      case '.jpg':
+      case '.jpeg':
+        return 'image/jpeg'
+      case '.tiff':
+        return 'image/tiff'
+      case '.gif':
+        return 'image/gif'
+      default:
+        return 'application/octet-stream'
+    }
+  }
+}