build+docs: switch to python3, refresh FAQ and INSTALL documents

Refs: #5095
Change-Id: Icdc0e9463b28c07783edbe392a9bc47136947e3b
diff --git a/.travis.yml b/.travis.yml
index b99ea35..16eb7b6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -93,12 +93,7 @@
         export DISABLE_ASAN=yes
         ;;
     esac
-    if [[ ${TRAVIS_OS_NAME} == osx ]]; then
-      # Do not waste time upgrading useless packages
-      brew pin cgal gdal postgis sfcgal || true
-      # Ensure /usr/local/opt/openssl exists
-      brew reinstall openssl || true
-    elif [[ ${TRAVIS_OS_NAME} == linux ]]; then
+    if [[ ${TRAVIS_OS_NAME} == linux ]]; then
       sudo sysctl -e -w net.ipv6.conf.all.disable_ipv6=0
     fi
   - ${CXX:-c++} --version