travis: Cache maven local repo to speedup builds
travis: Cache maven local repo to speedup builds

Signed-off-by: Michael Jeanson <bd309e36450a88bf12e0e03a6bd0dbd5b2cf425c@efficios.com>

alexmonthy/lttng-scope,lttng/lttng-scope,alexmonthy/lttng-scope,lttng/lttng-scope,alexmonthy/lttng-scope,lttng/lttng-scope,lttng/lttng-scope