[gnome-continuous] Use the appropriate option for gtk's print backends

[Emmanuele Bassi <ebassi src gnome org>]

commit 4ffc8447b686342c75e6658d35e3b4b93a08e566
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sun Mar 18 18:50:01 2018 +0000

    Use the appropriate option for gtk's print backends
    
    The option is `print-backends`, not, `printbackends`.

 manifest.json |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/manifest.json b/manifest.json
index 1f88b2f..16970e1 100644
--- a/manifest.json
+++ b/manifest.json
@@ -625,7 +625,7 @@
                  "config-opts": ["-Ddocumentation=false",
                                  "-Dman-pages=false",
                                  "-Dintrospection=true",
-                                 "-Dprintbackends=file,lpr"],
+                                 "-Dprint-backends=file,lpr"],
                  "irc_room": "gtk+"},
 
                {"src": "fd:plymouth",