Change context import to system context

[vanship82]

go-grpc-prometheus/server_metrics.go

Line 5 in c225b8c

 "golang.org/x/net/context" 

It breaks the build with grpc v1.18.0

[Frederic Branczyk]

I'm happy with changing to the core package. Wdyt @bwplotka ?

[vanship82]

Thanks! Here is another one 👍

go-grpc-prometheus/client_metrics.go

Line 7 in 68e3a13

 "golang.org/x/net/context" 

[Bartlomiej Plotka]

I think the Golang compatibility is the key question here. We need to choose one (:

Either deprecate old Golang (I think 1.6 or something?) or not allow grpc v1.18.0 ;p

I feel like a new release that goes with gRPC on golang compatiblity side is way to go with this. 👍

[Frederic Branczyk]

Seems like we're in agreement :) let's update