go CI fails with "cannot find package "golang.org/x/tools/go/packages" in any of ..."

mkdir -p src/gen
/thrift/src/compiler/cpp/thrift -out src/gen --gen go:thrift_import=thrift ThriftTest.thrift
[WARNING:/thrift/src/test/go/ThriftTest.thrift:45] No generator named 'noexist' could be found!
[WARNING:/thrift/src/test/go/ThriftTest.thrift:47] cpp generator does not accept 'noexist' as sub-namespace!
/thrift/src/compiler/cpp/thrift -out src/gen --gen go:thrift_import=thrift ../StressTest.thrift
[WARNING:/thrift/src/test/StressTest.thrift:31] Consider using the more efficient "binary" type instead of "list<byte>".
[WARNING:/thrift/src/test/StressTest.thrift:31] Consider using the more efficient "binary" type instead of "list<byte>".
GOPATH=`pwd` /usr/local/bin/go get github.com/golang/mock/gomock || true
sed -i 's/\"context\"/\"golang.org\/x\/net\/context\"/g' src/github.com/golang/mock/gomock/controller.go || true
GOPATH=`pwd` /usr/local/bin/go get github.com/golang/mock/gomock
ln -nfs ../../../lib/go/thrift src/thrift
touch gopath
GOPATH=`pwd` /usr/local/bin/go install github.com/golang/mock/mockgen
src/github.com/golang/mock/mockgen/parse.go:34:2: cannot find package "golang.org/x/tools/go/packages" in any of:
	/usr/local/go/src/golang.org/x/tools/go/packages (from $GOROOT)
	/thrift/src/test/go/src/golang.org/x/tools/go/packages (from $GOPATH)
Makefile:673: recipe for target 'genmock' failed
make[2]: *** [genmock] Error 1
make[2]: Leaving directory '/thrift/src/test/go'
Makefile:633: recipe for target 'check-recursive' failed
make[1]: *** [check-recursive] Error 1
make[1]: Leaving directory '/thrift/src/test'
Makefile:686: recipe for target 'check-recursive' failed
make: *** [check-recursive] Error 1
travis_time:end:0aae51b0:start=1556474908740752565,finish=1556476800695330969,duration=1891954578404
[0K[31;1mThe command "build/docker/run.sh" exited with 2.[0m