npmignore .cache, .github, .lgtm, and _gh-pages

I don't think there is any value in distributing these files in the
package.

.npmignore

@@ -32,13 +32,17 @@ node_modules
 # Optional REPL history
 .node_repl_history
 
+.cache
+.github
+.lgtm
 .storybook
 .storybook-css
+_gh-pages
 examples
+MAINTAINERS
 public
 react-dates-demo.gif
 stories
 test
 css
 !lib/css
-