Fix building with DUB and static libraries

**Summary**
I had link errors when building whatever using logger with DUB. Fixed by tweaking package.json

**To reproduce:** make a DUB project using logger >=0.0.1, then type "dub".
DUB version: v0.9.21
DMD version: v2.065

**Example of error messages:**

    Error 42: Symbol Undefined _D3std6logger6Logger5errorMFNebAyaiAyaAyaAyaZC3std6logger6Logger (@trusted std.logger.Logger std.logger.Logger.error(bool, immutable(char)[], int, immutable(char)[], immutable(char)[], immutable(char)[]))

**Two possible fixes:**
1. remove the "configurations" key from package.json (I like it since DUB is able to see it's a library)
2. change "sourceLibrary" into just "library"