component/protobuf: add missing rpath to zlib

component/protobuf/buildout.cfg

 [buildout]
+extends =
+  ../zlib/buildout.cfg
+
 parts = protobuf
 
 [protobuf]
@@ -6,9 +9,13 @@ recipe = slapos.recipe.cmmi
 shared = true
 url = https://github.com/google/protobuf/releases/download/v3.4.0/protobuf-python-3.4.0.tar.gz
 md5sum = 0820cc2e56d71aef8e99794fcbd184cd
+environment =
+  LDFLAGS=-Wl,-rpath=${zlib:location}/lib
 
 [protobuf-cpp]
 recipe = slapos.recipe.cmmi
 shared = true
 url = https://github.com/google/protobuf/releases/download/v3.4.0/protobuf-cpp-3.4.0.tar.gz
 md5sum = 6d59dad503bea5ad420fd09ddad84481
+environment =
+  LDFLAGS=-Wl,-rpath=${zlib:location}/lib
\ No newline at end of file