Fix YAML colour schemes to be Psych readable

Trying to load originals with Psych:
[ytti@lintukoto ~]% pry -r yaml
[1] pry(main)> YAML.load_file "/home/ytti/tmp/keybox/resources/light_bg.color_scheme.yaml"
Psych::SyntaxError: (/home/ytti/tmp/keybox/resources/light_bg.color_scheme.yaml): did not find expected node content while parsing a flow node at line 19 column 19

Using 'Syck' same file works just fine. However in Ruby2.0 you cannot
switch to Sych anymore, but you have to use Psych.