Fix searching ignored directories for ripgrep

[shutosheep]

Currently projectile-ripgrep does not properly hide directories of projectile-globally-ignored-directories as mentioned in issue #1811 . projectile-ripgrep produces following arguments for searching.

rg  --fixed-strings --hidden --glob !TAGS --glob !^\.idea$ --glob !^\.vscode$ ...

I found that there are two problems:

• Both ignored file and directory name is not quoted with '
• Directory name includes regexp which I believe --glob option does not support
  • Looking at ripgrep's -g flag docstring, it says that it uses gitignore rules

In this PR, I made both globally ignored file and directory names to be quoted with ' and remove unnecessary regexp (^\ and $) from projectile-globally-ignored-directories. This results in making arguments such as...

rg  --fixed-strings --hidden --glob '!TAGS' --glob '!.idea' --glob '!.vscode' ...

resulting with ripgrep properly ignoring contents of projectile-globally-ignored-directories.

By the way I am new to emacs lisp, so feel free to edit my changes.

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