Gemfile.lock: update sprockets version

Apparently 2.11.0 has a vulnerability (CVE-2014-7819). I had
to hand-munge this one because "bundle update sprockets"
doesn't work (I think because sass-rails has a dependency on
2.11.0).

Author: peff

Gemfile.lock

@@ -204,14 +204,14 @@ GEM
     sass-rails (4.0.3)
       railties (>= 4.0.0, < 5.0)
       sass (~> 3.2.0)
-      sprockets (~> 2.8, <= 2.11.0)
+      sprockets (~> 2.8, <= 2.11.3)
       sprockets-rails (~> 2.0)
     sawyer (0.8.1)
       addressable (>= 2.3.5, < 2.6)
       faraday (~> 0.8, < 1.0)
     shoulda-matchers (3.1.2)
       activesupport (>= 4.0.0)
-    sprockets (2.11.0)
+    sprockets (2.11.3)
       hike (~> 1.2)
       multi_json (~> 1.0)
       rack (~> 1.0)