libgpaste-applet: fix update

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: do not use markup

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
libgpaste-applet: fix warning

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>