fix(pseudopatterns): use the template instead of the pseudo data file…

[mfranzke]

… for template rendering #1308

Closes #1308

Summary of changes:

Credits go to @AdrianRichardson who made the suggestion within https://gitter.im/pattern-lab/node?at=600c7cb597132e2480fcafe5:

(...) when rendering, pattern.relPath is used as the source file passed to Twing. However, when rendering a pseudo pattern, the value of pattern.relPath is the JSON/YAML file so the wrong thing is used for the template.

It looks like the required value is under pattern.basePattern.relPath when processing a pseudo-pattern. Changing

patternlab-node/packages/engine-twig/lib/engine_twig.js

Line 133 in d18ddac

var patternPath = pattern.relPath;

to var patternPath = pattern.basePattern ? pattern.basePattern.relPath : pattern.relPath; seems to fix it.

Setup:

atoms/test/base-template.twig with atoms/test/base-template~pseudo.json will output just a copy of atoms/test/base-template~pseudo.json as atoms-base-template-pseudo.rendered.html, not the parsed HTML from the base-template.twig. It works OK with no pseudo pattern, ie atoms/test/base-template.twig and atoms/test/base-template.json