Make sure Spacemacs searches with git grep

See: syl20bnr/spacemacs#2162

spacemacs

@@ -286,7 +286,7 @@ values."
    ;; List of search tool executable names. Spacemacs uses the first installed
    ;; tool of the list. Supported tools are `ag', `pt', `ack' and `grep'.
    ;; (default '("ag" "pt" "ack" "grep"))
-   dotspacemacs-search-tools '("ag" "pt" "ack" "grep")
+   dotspacemacs-search-tools '("grep" "ag" "pt" "ack")
    ;; The default package repository used if no explicit repository has been
    ;; specified with an installed package.
    ;; Not used for now. (default nil)
@@ -316,7 +316,9 @@ layers configuration.
 This is the place where most of your configurations should be done. Unless it is
 explicitly specified that a variable should be set before a package is loaded,
 you should place your code here."
-  (setq-default vc-follow-symlinks t)
+  (setq-default
+   projectile-use-git-grep t
+   vc-follow-symlinks t)
   (global-set-key (kbd "s-t") 'helm-projectile-find-file)
   (define-key evil-normal-state-map (kbd "C-a") 'evil-numbers/inc-at-pt)
   (define-key evil-normal-state-map (kbd "C-x") 'evil-numbers/dec-at-pt)