ci: Build against the 1.x branch of libcangjie

libcangjie master broke its API, so we can't build the 1.x branch of
pycangjie against libcangjie master any more.

This is all perfectly expected though, but we need to tell Travis about
it.
Merge pull request #22 from Cangjians/tests

ci: Build against the 1.x branch of libcangjie