Update to Grape v1.4.0

Grape v1.4.0 fixes a memory leak that was present in v1.3.3 (https://github.com/ruby-grape/grape/pull/2084).

https://github.com/ruby-grape/grape/pull/1520 introduced a regression that always caused the Cache-Control HTTP header to be set to no-cache, even if the response wasn't a stream. To fix this, we only set HTTP headers if there is an actual stream.

This brings in https://github.com/ruby-grape/grape/pull/2088 to fix https://github.com/ruby-grape/grape/issues/2087.

Full list of changes:

• https://github.com/ruby-grape/grape/blob/master/CHANGELOG.md
• https://github.com/ruby-grape/grape/compare/v1.3.3..v1.4.0