liboauth: add `nss3` path to liboauth.la

Fixes the following libgdata build error:
```
  CCLD     gdata/libgdata.la
/nix/store/5kdjp8200hazaydx0dmwn5qghqkyi3py-binutils-2.23.1/bin/ld: cannot find -lssl3
/nix/store/5kdjp8200hazaydx0dmwn5qghqkyi3py-binutils-2.23.1/bin/ld: cannot find -lsmime3
/nix/store/5kdjp8200hazaydx0dmwn5qghqkyi3py-binutils-2.23.1/bin/ld: cannot find -lnss3
/nix/store/5kdjp8200hazaydx0dmwn5qghqkyi3py-binutils-2.23.1/bin/ld: cannot find -lnssutil3
collect2: error: ld returned 1 exit status
```