Fix FindNettle usage to actually check version.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8f2f0dc..6548401 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -35,8 +35,8 @@
   set(COMMONCRYPTO_FOUND FALSE)
 endif()
 if(ENABLE_GNUTLS)
-  include(FindNettle 3.0)
-  include(FindGnuTLS)
+  find_package(Nettle 3.0)
+  find_package(GnuTLS)
 else()
   set(GNUTLS_FOUND FALSE)
 endif()