build(package): exclude non-essentials files (#21)

https://www.reddit.com/r/PHP/comments/2jzp6k/i_dont_need_your_tests_in_my_production

Author: vinkla

.gitattributes

@@ -0,0 +1,11 @@
+* text=auto
+
+/tests export-ignore
+/.editorconfig export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore
+/.npmrc export-ignore
+/codecov.yml export-ignore
+/package.json export-ignore
+/dependencies.yml export-ignore
+/README.md export-ignore