Add .gitattributes file so the packaged zip becomes cleaner

See: jisaacks/GitGutter@a8beea5

.gitattributes

@@ -0,0 +1,21 @@
+# Stuff not being exported to ZIP and therefore
+# prevented from being packed into LSP.sublime-package
+
+## git
+.github/          export-ignore
+gh-pages/         export-ignore
+*.git             export-ignore
+*.gitignore       export-ignore
+*.gitattributes   export-ignore
+
+## unit testing
+tests/            export-ignore
+unittesting.json  export-ignore
+
+## other configs
+stubs/            export-ignore
+.travis.yml       export-ignore
+.appveyor.yml     export-ignore
+.coveragerc       export-ignore
+*.ini             export-ignore
+*.cfg             export-ignore