[DRE-maint] ruby-grape-msgpack is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-grape-msgpack 0.2.0-1 is marked for autoremoval from testing on 2018-03-08

It (build-)depends on packages with these RC bugs:
877257: ruby-grape: FTBFS with ruby2.3 and ruby-rack-test 0.7
888127: ruby-grape-entity: FTBFS on ruby2.5: syntax error, unexpected '{'
888190: ruby-mustermann19: FTBFS on ruby2.5: TypeError: Integer
890257: ruby-grape: FTBFS with ruby2.3 and ruby-rack-test 0.7