prepare release 0.33.0 (ruby-grape#749)

- aligns ruby versions for travis, rubocop and the gem itself

Author: LeFnord

.travis.yml

@@ -14,7 +14,7 @@ env:
   - MODEL_PARSER=grape-swagger-entity
   - MODEL_PARSER=grape-swagger-representable
   - GRAPE_VERSION=1.0.3
-  - GRAPE_VERSION=1.2.2
+  - GRAPE_VERSION=1.2.4
   - GRAPE_VERSION=HEAD
 
 matrix:

CHANGELOG.md

@@ -170,7 +170,6 @@
 * [#756](https://github.com/ruby-grape/grape-swagger/pull/756): Fix reference creation when custom type for documentation is provided - [@bikolya](https://github.com/bikolya).
 * [#764](https://github.com/ruby-grape/grape-swagger/pull/764): Fix root element for multi-word entities - [@bikolya](https://github.com/bikolya).
 
-
 ### 0.33.0 (June 21, 2019)
 
 #### Fixes