Remove RC from changelog version

Adding RC would require updating other scripts to support it.  For the
purpose of the changelog just using 4.0.4 should suffice.  Might Add
support for this later.

help/changelog

@@ -1,4 +1,4 @@
-=== 4.0.4 RC (2019-05-13)
+=== 4.0.4 (2019-05-13)
 
 * Update qt/platform.py to support other Unix style OSes (#444)
 * Fix font size scaling issue in properties dialog [qt] (#504)