escaped the special characters and added a dot

Author: nawu

build_tools/mac-install-gflags.sh

@@ -22,4 +22,4 @@ echo ""
 echo "-----------------------------------------------------------------------------"
 echo "|                         Installation Completed                            |"
 echo "-----------------------------------------------------------------------------"
-echo "Please run `. ~/.bash_profile` to be able to compile with gflags"
+echo "Please run \`. ~/.bash_profile\` to be able to compile with gflags"