Update .gitattributes to latest proposal

Author: slozier

.gitattributes

@@ -46,15 +46,7 @@ tests/suite/file_without_BOM.txt -text
 *.pdf -text
 
 # Hide certain languages from GitHub Linguist
-*.pck linguist-detectable=false
-*.c linguist-detectable=false
-
-*.bat linguist-detectable=false
-*.cmd linguist-detectable=false
-*.ps1 linguist-detectable=false
-*.1 linguist-detectable=false
-*.2 linguist-detectable=false
-*.3 linguist-detectable=false
-*.4 linguist-detectable=false
-
-*.html linguist-documentation=true
+* linguist-detectable=false
+*.cs linguist-detectable
+*.py linguist-detectable
+src/core/IronPython.StdLib/lib/** linguist-vendored