[pitivi/1.0] flatpak: Fix pylint installation in sandbox

[Alexandru Băluț <alexbalut src gnome org>]

commit 4bfa104c6904198c97858a5b08fa7c73cd380e60
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Wed Feb 7 22:07:16 2018 +0100

    flatpak: Fix pylint installation in sandbox

 build/flatpak/pitivi-flatpak |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/build/flatpak/pitivi-flatpak b/build/flatpak/pitivi-flatpak
index c03e1f5..5d0538d 100755
--- a/build/flatpak/pitivi-flatpak
+++ b/build/flatpak/pitivi-flatpak
@@ -564,9 +564,10 @@ class PitiviFlatpak:  # pylint: disable=too-many-instance-attributes
         # installed in the development pyvenv which is outside the sandbox
         # because git-pylint-commit-hook needs to import pylint.config.
         if fresh_install or self.update:
-            pip_modules = "pylint"
+            pip_modules = ["pylint"]
             print("Installing development tools in the sandbox: %s" % pip_modules)
-            self.run_in_sandbox("pip3 install -U --user %s" % pip_modules, exit_on_failure=True)
+            self.run_in_sandbox("pip3", "install", "-U", "--user", *pip_modules,
+                                exit_on_failure=True)
 
         if not self.check and not self.update:
             self.run_in_sandbox(*self.args, exit_on_failure=True)