Enable user namespace cloning

Author: Forest Hoffman

.travis.yml

@@ -50,7 +50,8 @@ before_install:
     libnss3
     lsb-release
     xdg-utils
-    wget; fi
+    wget;
+    sysctl -w kernel.unprivileged_userns_clone=1; fi
 - npm install -g yarn@1.12.3
 script:
 - scripts/build.sh