feat(agent): send User-Agent

fix(scripts): change default node version from 6 to 8

chore(package): update optional dependencies to make sure the package…

… works with yarn

chore(issue template): add an issue template

chore(package): update v8-profiler to 5.7.11

chore(package): update native deps

chore(packages): update

fix(mysql): instrument pool.getConnection properly

fix(mysql): instrument pool.getConnection properly