[gnome-build-meta] .gitlab-ci.yml: Use the bst version specify in the CI, not the one from the image

[Javier Jardón Cabezas <jjardon src gnome org>]

commit e9416544fcd8aa0cdb5f6f30c7e353da239bcb4f
Author: Javier Jardón <jjardon gnome org>
Date:   Sat Feb 24 19:30:22 2018 +0000

    .gitlab-ci.yml: Use the bst version specify in the CI, not the one from the image

 .gitlab-ci.yml | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 51ba2fd..ab99e45 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -12,8 +12,10 @@ stages:
   - build
 
 before_script:
-  - git clone https://gitlab.com/BuildStream/buildstream.git
+  # Remove any installed buildstream binary
+  - pip3 uninstall -y buildstream
   # Use specific version of BuildStream
+  - git clone https://gitlab.com/BuildStream/buildstream.git
   - git -C buildstream/ checkout $BST_SHA
   - pip3 install buildstream