File level using for causes instrument error

[ddnexus]

using SomeLib for SomeType;

FIle level "using for" declaration is a feature in recent solidity, but an issue for solidity-coverage.

If you put it inside a library it will be ok for both, so it's a minor glitch with a possible workaround, but it's worth an issue.

[cgewecke]

Have added a test for this in #831 and it looks like this works now. This syntax might have been unsupported by solidity-parser/parser at some point.

Closing, please just ping if anyone runs into this and can provide an example which fails.