upgrade(GUI): electron to v1.2.6 (#561)
upgrade(GUI): electron to v1.2.6 (#561)

This version contains a GNU/Linux fix there the image extension was
changed by the dialog.

Change-Type: patch
Changelog-Entry: Fix `ENOENT` error when selecting certain images with multiple extensions on GNU/Linux.
See: https://github.com/electron/electron/issues/6305
Signed-off-by: Juan Cruz Viotti <8493db2a4f45d66df375afe12f7eba59fe1c8d78@gmail.com>
resin-io/etcher,resin-io/herostratus,resin-io/resin-etcher,resin-io/etcher,resin-io/etcher,cedricve/etcher,cedricve/etcher,resin-io/herostratus,resin-io/etcher,resin-io/resin-etcher,cedricve/etcher,resin-io/etcher