Same as 2.7.0. We need more thread safe version that compatible with current gollum-lib gemspec

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

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-grit (2.6.9)
+    gitlab-grit (2.6.10)
       charlock_holmes (~> 0.6)
       diff-lcs (~> 1.1)
       mime-types (~> 1.15)

History.txt

-== 2.7.0
+== 2.6.10
   * Remove the `chdir:` option for thread-safety
   * Automatically set the `--work-tree=` Git option

VERSION

-2.6.9
+2.6.10