enable go race detector tests in CI pipeline

[zanuka]

travis.yml should have go test -v -race ./... included in script block

The race detector is integrated with the go tool chain. When the -race command-line flag is set, the compiler instruments all memory accesses with code that records when and how the memory was accessed, while the runtime library watches for unsynchronized accesses to shared variables. When such "racy" behavior is detected, a warning is printed.