Bump min JOSM version down (bumped up to fix test issue with signing keys)

Signed-off-by: Taylor Smock <tsmock@fb.com>

gradle.properties

@@ -1,5 +1,5 @@
 # The minimum JOSM version this plugin is compatible with (can be any numeric version
-plugin.main.version = 17023
+plugin.main.version = 16846
 # The JOSM version this plugin is currently compiled against
 # Please make sure this version is available at https://josm.openstreetmap.de/download
 # The special values "latest" and "tested" are also possible here, but not recommended.