move stencila to preassemble

Author: minrk

repo2docker/buildpacks/base.py

@@ -711,12 +711,8 @@ def get_preassemble_scripts(self):
         except FileNotFoundError:
             pass
 
-        return scripts
-
-    def get_assemble_scripts(self):
-        assemble_scripts = []
         if "py" in self.stencila_contexts:
-            assemble_scripts.extend(
+            scripts.extend(
                 [
                     (
                         "${NB_USER}",
@@ -728,7 +724,7 @@ def get_assemble_scripts(self):
                 ]
             )
         if self.stencila_manifest_dir:
-            assemble_scripts.extend(
+            scripts.extend(
                 [
                     (
                         "${NB_USER}",
@@ -741,7 +737,11 @@ def get_assemble_scripts(self):
                     )
                 ]
             )
-        return assemble_scripts
+        return scripts
+
+    def get_assemble_scripts(self):
+        """Return directives to run after the entire repository has been added to the image"""
+        return []
 
     def get_post_build_scripts(self):
         post_build = self.binder_path("postBuild")