Quick fixup for commit a8090c13

That commit is "Necessary legal steps for python subprocess32 shipping."
Forgot to install the required file. Hmm...

gpMgmt/Makefile

@@ -32,6 +32,7 @@ install: generate_greenplum_path_file
 	fi
 	if [ -e bin/ext/subprocess32.py ]; then \
 	    cp -p bin/ext/subprocess32.py $(DESTDIR)$(prefix)/lib/python ; \
+	    cp -p bin/ext/subprocess32-ChangeLog $(DESTDIR)$(prefix)/lib/python ; \
 	    cp -p bin/ext/_posixsubprocess.so $(DESTDIR)$(prefix)/lib/python ; \
 	fi