Mark Rails/SaveBang as unsafe autocorrect

We faced an issue where our custom `update` method call was changed to `update!` but the method name remained same in the method definition.

```ruby
def update
end

update!
```

```ruby
def update
end

update
```

So the cop is not safe for auto correct.

Author: prathamesh-sonpatki

CHANGELOG.md

@@ -13,6 +13,7 @@
 ### Changes
 
 * [#98](https://github.com/rubocop-hq/rubocop-rails/pull/98): Mark `Rails/ActiveRecordAliases` as `SafeAutoCorrect` false and disable autocorrect by default. ([@prathamesh-sonpatki][])
+* [#101](https://github.com/rubocop-hq/rubocop-rails/pull/101): Mark `Rails/SaveBang` as `SafeAutoCorrect` false and disable autocorrect by default. ([@prathamesh-sonpatki][])
 
 ## 2.2.1 (2019-07-13)
 

config/default.yml

@@ -404,6 +404,7 @@ Rails/SaveBang:
   VersionChanged: '0.59'
   AllowImplicitReturn: true
   AllowedReceivers: []
+  SafeAutoCorrect: false
 
 Rails/ScopeArgs:
   Description: 'Checks the arguments of ActiveRecord scopes.'

manual/cops_rails.md

@@ -2064,7 +2064,7 @@ ConvertTry | `false` | Boolean
 
 Enabled by default | Safe | Supports autocorrection | VersionAdded | VersionChanged
 --- | --- | --- | --- | ---
-Disabled | Yes | Yes  | 0.42 | 0.59
+Disabled | Yes | Yes (Unsafe) | 0.42 | 0.59
 
 This cop identifies possible cases where Active Record save! or related
 should be used instead of save because the model might have failed to