test: Fix Travis infinite recursion breakage

I swear, I thought I'd run the tests again before commit
89c3b15. Previously I'd had a `_COVERAGE_RUN`
check in the same statement as the `TRAVIS_OS_NAME` check, but took it out. This
replaces it, and should make Travis healthy and happy.

Author: mbland

scripts/test

@@ -69,7 +69,7 @@ _test() {
     shift
     local tests=($(@go 'glob' "${__GO_TEST_GLOB_ARGS[@]}" "$@"))
     @go 'edit' "${tests[@]}"
-  elif [[ "$TRAVIS_OS_NAME" == 'linux' ]]; then
+  elif [[ "$_COVERAGE_RUN" != 'true' && "$TRAVIS_OS_NAME" == 'linux' ]]; then
     # Collect coverage by default on Travis. Doesn't seem to slow anything down
     # substantially.
     _test '--coverage' "$@"