Resolve dependecies correctly

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

Gemfile.lock

 PATH
   remote: .
   specs:
-    gitlab-grit (2.7.3)
+    gitlab-grit (2.8.0)
       charlock_holmes (~> 0.6)
       diff-lcs (~> 1.1)
-      mime-types (~> 2.6)
+      mime-types (>= 1.16, < 3)
       posix-spawn (~> 0.3)
 GEM
@@ -22,7 +22,7 @@ GEM
     diff-lcs (1.1.3)
     metaclass (0.0.1)
     method_source (0.8.1)
-    mime-types (1.18)
+    mime-types (2.6.2)
     mocha (0.13.2)
       metaclass (~> 0.0.1)
     multi_json (1.7.2)
@@ -62,3 +62,6 @@ DEPENDENCIES
   pry
   rake
   rspec (~> 2.11)
+
+BUNDLED WITH
+   1.11.2

gitlab-grit.gemspec

@@ -16,7 +16,7 @@ Gem::Specification.new do |s|
   s.add_dependency("charlock_holmes", "~> 0.6")
   s.add_dependency('posix-spawn', "~> 0.3")
-  s.add_dependency('mime-types', "~> 2.6")
+  s.add_dependency('mime-types', ">= 1.16", "< 3")
   s.add_dependency('diff-lcs', "~> 1.1")
   s.add_development_dependency('mocha')
 end