Try to fix syntax highlighting on github

github-linguist/linguist#3677
My understanding is that github uses linguist to identify what type of source file.
And there are two problems:
- The syntax highlighter used by linguist when it gets the wrong file type doesn't work with githubs regex engine.
- And Linguist doesn't correctly identify the jsx files as jsx.

I saw this gitattributes fix mentioned, so I'm giving it a try.

.gitattributes

@@ -0,0 +1 @@
+*.js linguist-language=JSX