Bump test-unit from 3.3.0 to 3.3.1 (publiclab#458)

Bumps [test-unit](https://github.com/test-unit/test-unit) from 3.3.0 to 3.3.1.
- [Release notes](https://github.com/test-unit/test-unit/releases)
- [Commits](test-unit/test-unit@3.3.0...3.3.1)

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

Gemfile.lock

@@ -106,7 +106,7 @@ GEM
       rack
       rake (>= 0.8.1)
     polyglot (0.3.5)
-    power_assert (1.1.3)
+    power_assert (1.1.4)
     rack (1.4.7)
     rack-cache (1.8.0)
       rack (>= 0.4)
@@ -170,7 +170,7 @@ GEM
     sqlite3 (1.4.0)
     term-ansicolor (1.7.1)
       tins (~> 1.0)
-    test-unit (3.3.0)
+    test-unit (3.3.1)
       power_assert
     therubyracer (0.12.3)
       libv8 (~> 3.16.14.15)