Bump gitlab-grit gem. Fixes another 500 error with submodules

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Gemfile.lock

@@ -165,7 +165,7 @@ GEM
       stringex (~> 1.5.1)
     gitlab-grack (1.0.1)
       rack (~> 1.4.1)
-    gitlab-grit (2.6.2)
+    gitlab-grit (2.6.3)
       charlock_holmes (~> 0.6.9)
       diff-lcs (~> 1.1)
       mime-types (~> 1.15)
@@ -274,7 +274,7 @@ GEM
       mime-types (~> 1.16)
       treetop (~> 1.4.8)
     method_source (0.8.1)
-    mime-types (1.25)
+    mime-types (1.25.1)
     minitest (4.7.4)
     modernizr (2.6.2)
       sprockets (~> 2.0)