Update image_optim from 0.14.0 -> 0.15.0

The latest version of the `image_optim` gem broke Overcommit's
`ImageOptim` pre-commit hook due to a change in the name of the
`BinNotFoundError` exception. Fix it and change the version constraint
in the gemspec.

Change-Id: Ie938de988887b2794115c35c45d654c7f7d9d678
Reviewed-on: http://gerrit.causes.com/42208
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: sds

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Overcommit Changelog
 
+## master (unreleased)
+
+* Update minimum version of `image_optim` gem to 0.15.0 (breaking change in
+  name of exception classes)
+
 ## 0.17.0
 
 * Change commit hook header text to bold instead of bold white so that it

lib/overcommit/hook/pre_commit/image_optim.rb

@@ -11,7 +11,7 @@ def run
       optimized_images =
         begin
           optimize_images(applicable_files)
-        rescue ::ImageOptim::BinNotFoundError => e
+        rescue ::ImageOptim::BinResolver::BinNotFound => e
           return :fail, "#{e.message}. The image_optim gem is dependendent on this binary."
         end
 

overcommit.gemspec

@@ -28,7 +28,7 @@ Gem::Specification.new do |s|
 
   s.add_dependency             'childprocess', '>= 0.5.1'
 
-  s.add_development_dependency 'image_optim', '~> 0.14.0'
+  s.add_development_dependency 'image_optim', '~> 0.15.0'
   s.add_development_dependency 'rspec', '~> 3.0'
   s.add_development_dependency 'rubocop', '0.25.0' # Pin for Travis builds
 end

spec/overcommit/hook/pre_commit/image_optim_spec.rb

@@ -12,7 +12,7 @@
 
   context 'when a dependency of image_optim is not installed' do
     before do
-      subject.stub(:optimize_images).and_raise(::ImageOptim::BinNotFoundError)
+      subject.stub(:optimize_images).and_raise(::ImageOptim::BinResolver::BinNotFound)
     end
 
     it { should fail_hook }