Remove unnecessary imageoptim dependency

Gemfile

@@ -8,6 +8,5 @@ gem "middleman-livereload"
 gem "middleman-minify-html"
 gem "middleman-syntax"
 gem 'middleman-gh-pages'
-gem 'middleman-imageoptim'
 
 gem "redcarpet"

Gemfile.lock

@@ -40,9 +40,7 @@ GEM
     erubis (2.7.0)
     eventmachine (1.0.8)
     execjs (2.6.0)
-    exifr (1.2.3.1)
     ffi (1.9.10)
-    fspath (2.1.1)
     haml (4.0.7)
       tilt
     hike (1.2.3)
@@ -51,17 +49,6 @@ GEM
     htmlcompressor (0.2.0)
     http_parser.rb (0.6.0)
     i18n (0.7.0)
-    image_optim (0.20.2)
-      exifr (~> 1.1, >= 1.1.3)
-      fspath (~> 2.1)
-      image_size (~> 1.3)
-      in_threads (~> 1.3)
-      progress (~> 3.0, >= 3.0.1)
-    image_optim_pack (0.2.1.20151002)
-      fspath (~> 2.1)
-      image_optim (~> 0.19)
-    image_size (1.4.1)
-    in_threads (1.3.1)
     json (1.8.3)
     kramdown (1.9.0)
     listen (3.0.3)
@@ -99,10 +86,6 @@ GEM
       tilt (~> 1.4.1, < 2.0)
     middleman-gh-pages (0.0.3)
       rake (> 0.9.3)
-    middleman-imageoptim (0.2.1)
-      image_optim (~> 0.20.2)
-      image_optim_pack (~> 0.2.1)
-      middleman-core (>= 3.1)
     middleman-livereload (3.4.3)
       em-websocket (~> 0.5.1)
       middleman-core (>= 3.3)
@@ -130,7 +113,6 @@ GEM
       tilt (~> 1.4.1)
     padrino-support (0.12.5)
       activesupport (>= 3.1)
-    progress (3.1.0)
     rack (1.6.4)
     rack-livereload (0.3.16)
       rack
@@ -174,7 +156,6 @@ DEPENDENCIES
   middleman-autoprefixer
   middleman-blog
   middleman-gh-pages
-  middleman-imageoptim
   middleman-livereload
   middleman-minify-html
   middleman-syntax

config.rb

@@ -73,7 +73,6 @@ configure :build do
     .woff
   ]}
   set :haml, {ugly: true, attr_wrapper: '"'}
-  activate :imageoptim
   activate :minify_css
   activate :minify_html do |html|
     html.remove_quotes = false