core: Update tests; fix bugs

[cxw42]

• Update core-tests submodule
• Do not look for comments in values (editorconfig/specification#31)
• Update property key and value limits (editorconfig/editorconfig-core-test#41)
• Fix nested-braces error (fixes #160)

[cxw42]

The CI failure was a timeout --- #200

[cxw42]

Merging even given the Appveyor timeout since it looks like it would have worked if it hadn't hit the timeout.