Bump rspec from 3.12.0 to 3.13.0

Bumps [rspec](https://github.com/rspec/rspec-metagem) from 3.12.0 to 3.13.0.
- [Commits](rspec/rspec-metagem@v3.12.0...v3.13.0)

---
updated-dependencies:
- dependency-name: rspec
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Gemfile.lock

@@ -1,27 +1,27 @@
 PATH
   remote: .
   specs:
-    ice_age (0.2.0)
+    ice_age (0.0.1)
 
 GEM
   remote: https://rubygems.org/
   specs:
     byebug (11.1.3)
-    diff-lcs (1.5.0)
+    diff-lcs (1.5.1)
     docile (1.4.0)
-    rspec (3.12.0)
-      rspec-core (~> 3.12.0)
-      rspec-expectations (~> 3.12.0)
-      rspec-mocks (~> 3.12.0)
-    rspec-core (3.12.0)
-      rspec-support (~> 3.12.0)
-    rspec-expectations (3.12.0)
+    rspec (3.13.0)
+      rspec-core (~> 3.13.0)
+      rspec-expectations (~> 3.13.0)
+      rspec-mocks (~> 3.13.0)
+    rspec-core (3.13.0)
+      rspec-support (~> 3.13.0)
+    rspec-expectations (3.13.1)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.12.0)
-    rspec-mocks (3.12.0)
+      rspec-support (~> 3.13.0)
+    rspec-mocks (3.13.1)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.12.0)
-    rspec-support (3.12.0)
+      rspec-support (~> 3.13.0)
+    rspec-support (3.13.1)
     simplecov (0.22.0)
       docile (~> 1.1)
       simplecov-html (~> 0.11)