remove -Werror compiler option in ruby Makefile to build on mac in opt configuration

src/ruby/ext/grpc/extconf.rb

@@ -102,7 +102,6 @@ $CFLAGS << ' -std=c99 '
 $CFLAGS << ' -Wall '
 $CFLAGS << ' -Wextra '
 $CFLAGS << ' -pedantic '
-$CFLAGS << ' -Werror '
 $CFLAGS << ' -Wno-format '
 
 output = File.join('grpc', 'grpc_c')