Minor grammatical update to CHANGES.txt and RELEASE.txt [ci skip]

Author: jcbrill

CHANGES.txt

@@ -13,7 +13,7 @@ RELEASE  VERSION/DATE TO BE FILLED IN LATER
       of _ListVariable class
 
   From Joseph Brill:
-    - Add an optional argument list string to configures CheckFunc method so
+    - Add an optional argument list string to configure's CheckFunc method so
       that the generated function argument list matches the function's
       prototype when including a header file. Fixes GH Issue #4320
 

RELEASE.txt

@@ -26,7 +26,7 @@ DEPRECATED FUNCTIONALITY
 CHANGED/ENHANCED EXISTING FUNCTIONALITY
 ---------------------------------------
 
-- Add an optional argument list string to configures CheckFunc method so
+- Add an optional argument list string to configure's CheckFunc method so
   that the generated function argument list matches the function's
   prototype when including a header file. Fixes GH Issue #4320