Add changelog entry

[skip ci]

Author: norio-nomura

CHANGELOG.md

@@ -33,6 +33,10 @@
   [Jacob Greenfield](https://github.com/Coder-256)
   [#2231](https://github.com/realm/SwiftLint/issues/2231)
 
+* Fix a crash when running with Swift 4.2.  
+  [Norio Nomura](https://github.com/norio-nomura)
+  [SR-7954](https://bugs.swift.org/browse/SR-7954)
+
 ## 0.26.0: Maytagged Pointers
 
 #### Breaking