Make tests that use mock_column more accurate (#48)

Columns that ActiveRecord gives us has String `#names`. Some tests pass
in a Symbol name into `mock_column` which is not accurate, so this PR
corrects that.

Follows up on:
#44 (comment)

Author: drwl

spec/lib/annotate_rb/annotate_models/annotate_models_annotating_a_file_frozen_spec.rb

@@ -12,8 +12,8 @@ class User < ActiveRecord::Base
       @klass = mock_class(:users,
         :id,
         [
-          mock_column(:id, :integer),
-          mock_column(:name, :string, limit: 50)
+          mock_column("id", :integer),
+          mock_column("name", :string, limit: 50)
         ])
       @schema_info = AnnotateRb::ModelAnnotator::AnnotationBuilder.new(@klass).build
     end
@@ -28,7 +28,7 @@ class User < ActiveRecord::Base
         annotate_one_file
 
         another_schema_info = AnnotateRb::ModelAnnotator::AnnotationBuilder.new(
-          mock_class(:users, :id, [mock_column(:id, :integer)])
+          mock_class(:users, :id, [mock_column("id", :integer)])
         ).build
 
         @schema_info = another_schema_info

spec/lib/annotate_rb/annotate_models/annotate_models_annotating_a_file_spec.rb

@@ -13,8 +13,8 @@ class User < ActiveRecord::Base
       @klass = mock_class(:users,
         :id,
         [
-          mock_column(:id, :integer),
-          mock_column(:name, :string, limit: 50)
+          mock_column("id", :integer),
+          mock_column("name", :string, limit: 50)
         ])
       @schema_info = AnnotateRb::ModelAnnotator::AnnotationBuilder.new(@klass).build
     end
@@ -102,8 +102,8 @@ class User < ActiveRecord::Base
           klass = mock_class(:users,
             :id,
             [
-              mock_column(:id, :integer),
-              mock_column(:foreign_thing_id, :integer)
+              mock_column("id", :integer),
+              mock_column("foreign_thing_id", :integer)
             ],
             [],
             [
@@ -124,8 +124,8 @@ class User < ActiveRecord::Base
           klass = mock_class(:users,
             :id,
             [
-              mock_column(:id, :integer),
-              mock_column(:foreign_thing_id, :integer)
+              mock_column("id", :integer),
+              mock_column("foreign_thing_id", :integer)
             ],
             [],
             [
@@ -149,7 +149,7 @@ class User < ActiveRecord::Base
       before do
         annotate_one_file position: :before
         another_schema_info = AnnotateRb::ModelAnnotator::AnnotationBuilder.new(
-          mock_class(:users, :id, [mock_column(:id, :integer)])
+          mock_class(:users, :id, [mock_column("id", :integer)])
         ).build
 
         @schema_info = another_schema_info
@@ -175,7 +175,7 @@ class User < ActiveRecord::Base
       before do
         annotate_one_file position: :after
         another_schema_info = AnnotateRb::ModelAnnotator::AnnotationBuilder.new(
-          mock_class(:users, :id, [mock_column(:id, :integer)])
+          mock_class(:users, :id, [mock_column("id", :integer)])
         ).build
 
         @schema_info = another_schema_info
@@ -214,8 +214,8 @@ class Foo::User < ActiveRecord::Base
       klass = mock_class(:foo_users,
         :id,
         [
-          mock_column(:id, :integer),
-          mock_column(:name, :string, limit: 50)
+          mock_column("id", :integer),
+          mock_column("name", :string, limit: 50)
         ])
       schema_info = AnnotateRb::ModelAnnotator::AnnotationBuilder.new(
         klass