Update ruby versions tested on evergreen and update rubygems version to fix error with ruby 2.5.0

Author: estolfo

.evergreen/.evg.yml

@@ -472,14 +472,10 @@ axes:
         display_name: ruby-2.3
         variables:
            RVM_RUBY: "ruby-2.3"
-      - id: "ruby-2.4.2"
-        display_name: ruby-2.4.2
+      - id: "ruby-2.5.0"
+        display_name: ruby-2.5.0
         variables:
-           RVM_RUBY: "ruby-2.4.2"
-#      - id: "jruby-9.1"
-#        display_name: jruby-9.1
-#        variables:
-#           RVM_RUBY: "jruby-9.1"
+           RVM_RUBY: "ruby-2.5.0"
   - id: "os"
     display_name: OS
     values:

.evergreen/run-tests.sh

@@ -36,6 +36,9 @@ assert(ruby in "`ruby --version`")
 assert(version in "`ruby --version`")
 EOH
 
+echo 'updating rubygems'
+gem update --system
+
 gem install bundler