Ignore signing files

Change-Id: Ib318c3c1579ffb588fe17a33567866b89837e68a
Reviewed-on: http://gerrit.dmdirc.com/1789
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>

.gitignore

@@ -10,6 +10,7 @@ build-before-profiler.xml
 /junit*.properties
 /installer/output/*
 /installer/osx/compress-dmg
+/installer/signing/*
 /installer/windows/*.rc
 /installer/windows/*.inc
 /installer/windows/*.ico