Set version of ruaml.yaml to strictly less than 0.15.52.

This allows to use version 0.15.51 rather than 0.15.0 which is
required for Python 3.

Fixes #571.

1 files changed, 1 insertions, 1 deletions

diff --git a/setup.py b/setup.py
index 35b8245c9..cda0ebbcb 100755
--- a/setup.py
+++ b/setup.py
@@ -258,7 +258,7 @@ setup(name='BuildStream',
       install_requires=[
           'setuptools',
           'psutil',
-          'ruamel.yaml <= 0.15',
+          'ruamel.yaml < 0.15.52',
           'pluginbase',
           'Click',
           'blessings',