Update Sinatra to 1.4.5

Also update backports package, its current version is causing issues on
Ruby 2.1.3

Gemfile

@@ -1,6 +1,6 @@
 source "https://rubygems.org"
 
-gem "sinatra"
+gem "sinatra", '~> 1.4'
 gem "sinatra-contrib"
 gem "activesupport", '~> 3.2'
 gem "riak-client", :github => "5apps/riak-ruby-client", :branch => "invalid_uri_error"

Gemfile.lock

@@ -16,7 +16,7 @@ GEM
     activesupport (3.2.18)
       i18n (~> 0.6, >= 0.6.4)
       multi_json (~> 1.0)
-    backports (3.3.0)
+    backports (3.6.1)
     beefcake (0.3.7)
     builder (3.2.2)
     eventmachine (1.0.3)
@@ -49,7 +49,7 @@ GEM
     purdytest (1.0.0)
       minitest (~> 2.2)
     rack (1.5.2)
-    rack-protection (1.5.0)
+    rack-protection (1.5.3)
       rack
     rack-test (0.6.2)
       rack (>= 1.0)
@@ -60,7 +60,7 @@ GEM
     raindrops (0.13.0)
     rake (0.9.2.2)
     ruby-hmac (0.4.0)
-    sinatra (1.4.3)
+    sinatra (1.4.5)
       rack (~> 1.4)
       rack-protection (~> 1.4)
       tilt (~> 1.3, >= 1.3.4)
@@ -88,5 +88,5 @@ DEPENDENCIES
   rainbows
   rake
   riak-client!
-  sinatra
+  sinatra (~> 1.4)
   sinatra-contrib