Issue geerlingguy#1573: Update default drupal versions to 8.4.x.

Author: geerlingguy

example.drupal.make.yml

@@ -11,13 +11,13 @@ projects:
 
   # Core.
   drupal:
-    version: "8.3.4"
+    version: "8.4.0"
     # Use this if you need a working git repository of Drupal core instead of
     # the latest stable.
     # type: "core"
     # download:
-    #   # Drupal core branch (e.g. "6.x", "7.x", "8.2.x", "8.3.x").
-    #   branch: "8.1.x"
+    #   # Drupal core branch (e.g. "6.x", "7.x", "8.3.x", "8.5.x").
+    #   branch: "8.4.x"
     #   working-copy: true
 
   # Other modules.

provisioning/docker/bin/install-drupal

@@ -4,13 +4,13 @@
 #
 # Usage:
 #   install-drupal [version]
-# [version] is optional, defaults to 8.3.x. Try 7.x, 7.55, 8.4.x, 8.3.2, etc.
+# [version] is optional, defaults to 8.4.x. Try 7.x, 7.55, 8.5.x, 8.3.2, etc.
 
 # Exit on any individual command failure.
 set -e
 
 # Setup.
-DRUPAL_VERSION="${1:-8.3.x}"
+DRUPAL_VERSION="${1:-8.4.x}"
 PROJECT_PATH='/var/www/drupalvm/drupal'
 
 # Create Drupal project directory.