updated thrift to latest Go library adding support for context

[basvanbeek]

In our addsvc example we supply a thrift transport which due to the api change in the Thrift Go library was broken.

This PR adds the support for context.Context as found in the latest Thrift Go library.

[basvanbeek]

travis has an unrelated build failure:

The command "go test -race -v ./..." exited with 0.
0.01s$ ./coveralls.bash
/home/travis/gopath/bin/gover
/home/travis/gopath/bin/goveralls
COVERALLS_TOKEN not set
The command "./coveralls.bash" exited with 1.

[peterbourgon]

What, that's garbage, the env var is clearly set in Travis..... argh

[peterbourgon]

We do not provide [repository environment variables] to untrusted builds, triggered by pull requests from another repository.

https://docs.travis-ci.com/user/environment-variables/#Defining-Variables-in-Repository-Settings

😠

[peterbourgon]

@basvanbeek Sorry, can you rebase on master?

[peterbourgon]

Leeroy Jenkins