Clean coding style for formula_field.

Thank you @lal_ for the patch, I have listed the following minor issues, which ideally phpcs should have returned, not sure why this didn't come. Anyways, if these can be fixed would be great.

1. +++ b/.idea/formula_field.iml
   @@ -0,0 +1,8 @@
   \ No newline at end of file
   

   Require a newline at end of file.

2. +++ b/.idea/misc.xml
   @@ -0,0 +1,6 @@
   \ No newline at end of file
   

   Require a new line at EOF.

3. +++ b/.idea/modules.xml
   @@ -0,0 +1,8 @@
   \ No newline at end of file
   

   Require a new line at EOF.

4. +++ b/.idea/vcs.xml
   @@ -0,0 +1,6 @@
   +<?xml version="1.0" encoding="UTF-8"?>
   +<project version="4">
   +  <component name="VcsDirectoryMappings">
   +    <mapping directory="$PROJECT_DIR$" vcs="Git" />
   +  </component>
   +</project>
   

   Don't think this file is required.

Infact, all`.idea` folder files are unnecessary. Can you please review it once.
Thanks!!

Thanks!
committed and pushed to 7.x-2.x branch. :)