Add .gitattributes

Ensures the line endings are lf on windows. CI was failing before this.

Only impacts developing ziglua. The build system doesn't convert line endings
so users of ziglua will not see an impact from this.

Author: natecraddock

.gitattributes

@@ -0,0 +1,6 @@
+*.zig text eol=lf
+*.zon text eol=lf
+*.lua text eol=lf
+*.cpp text eol=lf
+*.h text eol=lf
+*.patch text eol=lf