Fix that helm-git-grep-save-results can't work

fix the following error:
Symbol’s value as variable is void: grep-hit-face

features/helm-git-grep-save-result.feature

@@ -0,0 +1,18 @@
+Feature: Search a keyword and save search results
+  In order to search a keyword
+  As a user
+  I want to grep the keyword and save search results
+
+  Scenario: I save search results
+    Given I start an action chain
+    And I press "M-x"
+    And I type "helm-git-grep"
+    When I press "RET"
+    When I type "get_commit_format"
+    And I press "TAB"
+    And I press "C-n"
+    And I press "C-n"
+    And I press "C-n"
+    And I execute the action chain
+    Then I should be in buffer matching regexp "\*hggrep\*"
+    Then the cursor should be at line "5"

helm-git-grep.el

@@ -217,12 +217,9 @@ newline return an empty string."
                (helm-git-submodule-grep-command)))
     '()))
 
-(defvar grep-hit-face)
-
 (define-compilation-mode helm-git-grep-mode "Helm Git Grep"
   "Set up `wgrep' if exist."
-  (require' grep)
-  (set (make-local-variable 'compilation-error-face) grep-hit-face)
+  (set (make-local-variable 'compilation-error-face) compilation-info-face)
   (set (make-local-variable 'compilation-error-regexp-alist) grep-regexp-alist)
   (when (require 'wgrep nil t)
     (wgrep-setup-internal)))