Add a CI job to profile memory usage of commit

.travis.yml

@@ -6,18 +6,21 @@ rvm:
   - 2.3
   - 2.4
   - 2.5
+  - &latest_ruby 2.6
   - ruby-head
   - jruby-head
 #  - rbx-2
 
-sudo: false
-
 addons:
   apt:
     packages:
     - libgmp3-dev
 
 matrix:
+  include:
+    - rvm: *latest_ruby
+      script: bundle exec rake memory_profile:run
+      name: Profiling Memory Usage
   allow_failures:
     - rvm: ruby-head
     - rvm: jruby-head