Wording tweak

[skip ci]

Author: JonRowe

Changelog.md

@@ -4,7 +4,7 @@ Breaking Changes:
 
 * Ruby < 2.3 is no longer supported. (Phil Pirozhkov, #1349)
 * Extract monkey-patching `should_receive`/`stub` syntax. (Phil Pirozhkov, #1365)
-* Remove the deprecated `RSpec::Mocks::CannotSupportArgMutationsError`.
+* Remove the deprecated `RSpec::Mocks::CannotSupportArgMutationsError` constant.
   (Phil Pirozhkov, #1400)
 
 Bug Fixes: