* exporter(stackdriver): fix ExportSpans when ctx is not nil
- problem: if ctx is not, calling cancel() will panic
- nil Context already handled in newContextWithTimeout
- add with test
* update go.sum
* mock traceserver for traceclient
* make precommit
* - respect option.Context when get google cred and traceclient
* Revise with timeout, context
- rename blackbox tests package to stackdriver_test
- remove context is nil checking, add to initialization
- add tests for timeout
* automate building all the examples
the EXAMPLES variable was out of date - the stackdriver example wasn't
even built
let's automate it, so we don't need to remember about updating the
variable after adding a new example to the examples directory
* move jaeger example to example directory
this should be in the examples directory, so it can be built by the
make test during CI.
* switch to go 1.13
circle ci uses go 1.12 (which is the oldest 1.12 release) that
contains some bugs with module handling
let's switch to go 1.13.3, the latest go currently
* use a single valid revision of the project in go.mod files
this probably shouldn't be a problem since the switch to go 1.13 in
circle ci, but cleans up the mess and the use of bogus releases
