added note about nrgrpc version number bump
### Fixed
* A typographical error in the nrgrpc unit tests was fixed. Fixes [Issue #344](https://github.com/newrelic/go-agent/issues/344).
+ This updates the nrgrpc integration to version 1.3.1.
### Support Statement
New Relic recommends that you upgrade the agent regularly to ensure that you're getting the latest features and performance benefits. Additionally, older releases will no longer be supported when they reach end-of-life.
