cmake: add version, depend on libpjproject

Change-Id: I992cfff2e249f53b4f6ba2b989d4b5ed8e69aef2
diff --git a/dhtnet.pc.in b/dhtnet.pc.in
index 1e3faa6..efe9236 100644
--- a/dhtnet.pc.in
+++ b/dhtnet.pc.in
@@ -6,5 +6,5 @@
 Description: C++ peer to peer networking library
 Version: @VERSION@
 Requires: opendht >= 2.6
-Requires.private: pjproject
+Requires.private: libpjproject
 Cflags: -I${includedir}