Help: Explicitly say transaction, don't abbreviate to trans

The release notes need to make sense to people not so familiar with
each item. For those less familiar with RPM, spelling out "transaction"
makes this line item much clearer in isolation.

Help/release/3.18.rst

@@ -246,9 +246,9 @@ CPack
   installer is DPI-aware.
 
 * The :cpack_gen:`CPack RPM Generator` gained
-  :variable:`CPACK_RPM_PRE_TRANS_SCRIPT_FILE`
+  :variable:`CPACK_RPM_PRE_TRANS_SCRIPT_FILE` and
   :variable:`CPACK_RPM_POST_TRANS_SCRIPT_FILE`
-  variables to specify pre- and post-trans scripts.
+  variables to specify pre- and post-transaction scripts.
 
 Other
 -----