Updates conditional logic to use a case clause

.rubocop_todo.yml

@@ -1,15 +1,15 @@
 # This configuration was generated by `rubocop --auto-gen-config`
-# on 2015-04-23 09:39:10 -0700 using RuboCop version 0.30.0.
+# on 2015-04-23 11:18:24 -0700 using RuboCop version 0.30.0.
 # The point is for the user to remove these configuration records
 # one by one as the offenses are removed from the code base.
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
-# Offense count: 4
+# Offense count: 3
 Metrics/AbcSize:
   Max: 24
 
 # Offense count: 6
 # Configuration parameters: CountComments.
 Metrics/MethodLength:
-  Max: 12
+  Max: 13

lib/googleauth/compute_engine.rb

@@ -89,15 +89,16 @@ END
         c = options[:connection] || Faraday.default_connection
         c.headers = { 'Metadata-Flavor' => 'Google' }
         resp = c.get(COMPUTE_AUTH_TOKEN_URI)
-        if resp.status == 404
+        case resp.status
+        when 200
+          Signet::OAuth2.parse_credentials(resp.body,
+                                           resp.headers['content-type'])
+        when 404
           fail(Signet::AuthorizationError, NO_METADATA_SERVER_ERROR)
-        end
-        if resp.status != 200
+        else
           msg = "Unexpected error code #{resp.status}" + UNEXPECTED_ERROR_SUFFIX
           fail(Signet::AuthorizationError, msg)
         end
-        Signet::OAuth2.parse_credentials(resp.body,
-                                         resp.headers['content-type'])
       end
     end
   end