Add gitattributes for yml files

.gitattributes

@@ -6,3 +6,4 @@
 *.php   text eol=lf whitespace=blank-at-eol,blank-at-eof,space-before-tab,tab-in-indent,tabwidth=4 diff=php
 *.json  text eol=lf whitespace=blank-at-eol,blank-at-eof,space-before-tab,tab-in-indent,tabwidth=4
 *.test  text eol=lf whitespace=blank-at-eol,blank-at-eof,space-before-tab,tab-in-indent,tabwidth=4
+*.yml   text eol=lf whitespace=blank-at-eol,blank-at-eof,space-before-tab,tab-in-indent,tabwidth=2