tweak chaijs bot commit message

Author: keithamus

Makefile

@@ -97,7 +97,7 @@ nightly: clean plugins releases api-docs
 	@git config user.name "ChaiJs Bot"
 	@git config user.email "[email protected]"
 	@git add -f _data
-	@git commit -m '(nightly): build _data'
+	@git commit -m '(data): Auto build _data'
 	@git push "https://${GH_TOKEN}@github.com/chaijs/chai-docs" HEAD:refs/heads/gh-pages
 endif