Update `binding_of_caller` version

Updating this dependency fixed my Ruby 2.0 installation issues.

Gemfile.lock

@@ -94,7 +94,8 @@ GEM
     better_errors (0.3.2)
       coderay (>= 1.0.0)
       erubis (>= 2.7.0)
-    binding_of_caller (0.6.8)
+    binding_of_caller (0.7.1)
+      debug_inspector (>= 0.0.1)
     bootstrap-sass (2.2.1.1)
       sass (~> 3.2)
     builder (3.0.4)
@@ -132,6 +133,7 @@ GEM
     connection_pool (1.0.0)
     crack (0.3.1)
     daemons (1.1.9)
+    debug_inspector (0.0.2)
     devise (2.1.2)
       bcrypt-ruby (~> 3.0)
       orm_adapter (~> 0.1)