[pitivi] build: Answer automatically y/n questions when installing SDKs

[Thibault Saunier <tsaunier src gnome org>]

commit 7d0c355c93d1721e1b7c55abb2df21e15a22647e
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Tue Jul 17 23:46:18 2018 +0200

    build: Answer automatically y/n questions when installing SDKs
    
    For example:
    flatpak install --user flathub org.gnome.Platform.Locale 3.24 --reinstall
    Installing in user:
    org.gnome.Platform.Locale/x86_64/3.24 flathub fabbccbd2dae
    Is this ok [y/n]:

 build/flatpak/pitivi-flatpak | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/build/flatpak/pitivi-flatpak b/build/flatpak/pitivi-flatpak
index 83164556..78ce0f79 100755
--- a/build/flatpak/pitivi-flatpak
+++ b/build/flatpak/pitivi-flatpak
@@ -340,7 +340,7 @@ class FlatpakPackage(FlatpakObject):
             return
 
         self.flatpak("install", self.repo.name, self.name,
-                     self.branch, "--reinstall", show_output=True,
+                     self.branch, "--reinstall", "-y", show_output=True,
                      comment="Installing %s" % self.name)
 
     def update(self):