Update copyToClipBoard.js

Summary:
Since copy to clipboard functionality is now available in Linux, the comment above `copyToClipboard` function has been updated.
Closes https://github.com/facebook/react-native/pull/14773

Differential Revision: D5392372

Pulled By: hramos

fbshipit-source-id: 6e2668e1a89d37f9d5707fa36b3639895cd5bffd

local-cli/server/util/copyToClipBoard.js

@@ -17,7 +17,6 @@ const xsel = path.join(__dirname, 'external/xsel');
 fs.chmodSync(xsel, '0755');
 /**
  * Copy the content to host system clipboard.
- * This is only supported on Mac and Windows for now.
  */
 function copyToClipBoard(content) {
   switch (process.platform) {