Bump public_activity from 1.5.0 to 1.6.0 (AgileVentures#2487)

Bumps [public_activity](https://github.com/pokonski/public_activity) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/pokonski/public_activity/releases)
- [Changelog](https://github.com/chaps-io/public_activity/blob/1-6-stable/CHANGELOG.md)
- [Commits](https://github.com/pokonski/public_activity/commits)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot[bot]

Gemfile.lock

@@ -427,7 +427,7 @@ GEM
       pry (~> 0.10)
     pry-rails (0.3.6)
       pry (>= 0.10.4)
-    public_activity (1.5.0)
+    public_activity (1.6.0)
       actionpack (>= 3.0.0)
       activerecord (>= 3.0)
       i18n (>= 0.5.0)
@@ -445,7 +445,7 @@ GEM
     rack (2.0.5)
     rack-cache (1.8.0)
       rack (>= 0.4)
-    rack-test (1.0.0)
+    rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rack-timeout (0.5.1)
     railroady (1.5.3)