Added super_diff gem for improved diffing in tests

[numbata]

Leverage the super_diff gem to significantly enhance the clarity of diffs in failing RSpec tests.

Before:

       expected: [{"in"=>"header", "name"=>"postMultipleNestedParamsInBody", "required"=>true, "schema"=>{"$ref"=>"#/definitions/postMultipleNestedParamsInBody"}}]
            got: [{"in"=>"body", "name"=>"postMultipleNestedParamsInBody", "required"=>true, "schema"=>{"$ref"=>"#/definitions/postMultipleNestedParamsInBody"}}]

       (compared using eql?)

       Diff:
       @@ -1,4 +1,4 @@
       -[{"in"=>"header",
       +[{"in"=>"body",
          "name"=>"postMultipleNestedParamsInBody",
          "required"=>true,
          "schema"=>{"$ref"=>"#/definitions/postMultipleNestedParamsInBody"}}]

After:

       expected: [{ "name" => "postMultipleNestedParamsInBody", "in" => "header", "required" => true, "schema" => { "$ref" => "#/definitions/postMultipleNestedParamsInBody" } }]
            got: [{ "name" => "postMultipleNestedParamsInBody", "in" => "body", "required" => true, "schema" => { "$ref" => "#/definitions/postMultipleNestedParamsInBody" } }]

       (compared using eql?)

       Diff:

       ┌ (Key) ──────────────────────────┐
       │ ‹-› in expected, not in actual  │
       │ ‹+› in actual, not in expected  │
       │ ‹ › in both expected and actual │
       └─────────────────────────────────┘

         [
           {
             "name" => "postMultipleNestedParamsInBody",
       -     "in" => "header",
       +     "in" => "body",
             "required" => true,
             "schema" => {
               "$ref" => "#/definitions/postMultipleNestedParamsInBody"
             }
           }
         ]

[dblock]

Any reason not to require it all the time?

[numbata]

@dblock actually, no real reason. It can makes the diffs a bit longer, and if core code has issues the report can grow indefinitely.

[olivier-thatch]

👍 Nice change, I was also annoyed by how hard the diffs were to parse when working on #951.

[dblock]

CI looks borked :(

[numbata]

@dblock true. Because of fresh changes in ruby-dev. #954 should fix it.

[dblock]

Rebase this one?

[numbata]

@dblock done