It seems like the name of the downloaded jar has changed from compiler.jar to closure-compiler-v20160713.jar. The older versions of ClosureCompiler.js look for compiler.jar explicitly while 1.6.0looks for closure-compiler*. For users that specify their dependency on this library as ^1.5.3 or ~1.5.3, or any version below, the library doesn't work. It might make sense to pull in the jar finding code that was added in 1.6.0 to a 1.5.x minor so as not to break frozen builds.

This might not be the best solution and I'm sure you aren't totally in control of this but thought I would put it here for others.