fix(modules,contrib,thunderbird): grep binary file error

[jonasbadstuebner]

I saw that grep sometimes thinks the .msf file is a binary, so I added -a as a flag which tells grep to look inside binary files as well.
From man grep:

   File and Directory Selection
       -a, --text
              Process a binary file as if it were text; this is equivalent to the --binary-files=text option.

[tobi-wan-kenobi]

Thank you!