fix missing link dependency on libcpdb.so

[bakayu]

Fixes #88

Now libcpdb is correctly linked:

❯ readelf -d /usr/local/lib/libcpdb-frontend.so.3 | grep NEEDED | grep libcpdb
 0x0000000000000001 (NEEDED)             Shared library: [libcpdb.so.3]
 
❯ ldd /usr/local/lib/libcpdb-frontend.so.3 | grep cpdb
	libcpdb.so.3 => /usr/local/lib/libcpdb.so.3 (0x00007fa3c162d000)

[tillkamppeter]

@bakayu thanks a lot for the report and the fix.