debian/gbp.conf: drop pbuilder to avoid CI failure on salsa

debian/changelog

@@ -5,6 +5,8 @@ jruby-joni (2.1.29-1) unstable; urgency=medium
     - adjust dependency to jcodings 1.0.44
     - set Standards-Version: 4.4.0
   * add debian/salsa-ci.yml to exec CI on salsa.debian.org
+  * debian/gbp.conf
+    - drop pbuilder to avoid CI failure on salsa
 
  -- Hideki Yamane <henrich@debian.org>  Mon, 12 Aug 2019 12:54:28 +0900
 

debian/gbp.conf

@@ -10,6 +10,3 @@ color = auto
 upstream-tree = tag
 # uncomment this to automatically GPG sign tags:
 sign-tags = True
-
-pbuilder = True
-