ci: output Travis folding markers for each build stage

Makes build logs vastly more readable on Travis web UI

Change-Id: I00ebf48f80d73d7aad00b890d9c16c2254cb609c
diff --git a/.travis.yml b/.travis.yml
index d98dd24..570bb0e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -97,6 +97,8 @@
 before_script:
   - if [[ ${TRAVIS_OS_NAME} == linux ]]; then export NODE_LABELS="Linux Ubuntu Ubuntu-18.04"; fi
   - if [[ ${TRAVIS_OS_NAME} == osx ]]; then export NODE_LABELS="OSX OSX-${OSX_VERSION}"; fi
+  # do not waste time upgrading useless packages
+  - if [[ ${TRAVIS_OS_NAME} == osx ]]; then brew pin cgal gdal numpy postgis sfcgal || true; fi
   - if [[ ${OSX_VERSION} == 10.12 ]]; then brew update; fi
   # workaround for https://github.com/Homebrew/homebrew-core/issues/26358
   - if [[ ${OSX_VERSION} == 10.12 ]]; then brew outdated python || brew upgrade python; fi