Update CHANGELOG for #398 [ci skip]

Author: batter

.rspec

@@ -1,3 +1,2 @@
 --format progress
 --color
-

.travis.yml

@@ -10,6 +10,8 @@ env:
   - DB=postgres
   - DB=sqlite
 
+sudo: false
+
 before_script:
   - sh -c "if [ \"$DB\" = 'mysql' ]; then mysql   -e 'create database paper_trail_test;'; fi"
   - sh -c "if [ \"$DB\" = 'mysql' ]; then mysql   -e 'create database paper_trail_bar; '; fi"

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 3.1.0 (Unreleased)
 
+  - [#398](https://github.com/airblade/paper_trail/pull/398) - Only require the `RSpec` helper if `RSpec::Core` is required.
   - [#394](https://github.com/airblade/paper_trail/pull/394) - Add RSpec matcher `have_a_version_with` for easier testing.
 
 ## 3.0.3