Update development dependencies

This gets rid of a warning about a ffi vulnerability, and it makes it a
little easier to run tests in development using `rspec` and `cucumber`
directly (i.e. without running Appraisal).

Gemfile.lock

@@ -1,37 +1,37 @@
 PATH
   remote: .
   specs:
-    factory_bot (4.10.0)
+    factory_bot (4.11.0)
       activesupport (>= 3.0.0)
 
 GEM
   remote: https://rubygems.org/
   specs:
-    activemodel (5.1.4)
-      activesupport (= 5.1.4)
-    activerecord (5.1.4)
-      activemodel (= 5.1.4)
-      activesupport (= 5.1.4)
-      arel (~> 8.0)
-    activesupport (5.1.4)
+    activemodel (5.2.1)
+      activesupport (= 5.2.1)
+    activerecord (5.2.1)
+      activemodel (= 5.2.1)
+      activesupport (= 5.2.1)
+      arel (>= 9.0)
+    activesupport (5.2.1)
       concurrent-ruby (~> 1.0, >= 1.0.2)
-      i18n (~> 0.7)
+      i18n (>= 0.7, < 2)
       minitest (~> 5.1)
       tzinfo (~> 1.1)
     appraisal (2.1.0)
       bundler
       rake
       thor (>= 0.14.0)
-    arel (8.0.0)
-    aruba (0.14.2)
-      childprocess (~> 0.5.6)
+    arel (9.0.0)
+    aruba (0.14.6)
+      childprocess (>= 0.6.3, < 0.10.0)
       contracts (~> 0.9)
       cucumber (>= 1.3.19)
       ffi (~> 1.9.10)
       rspec-expectations (>= 2.99)
       thor (~> 0.19)
     builder (3.2.3)
-    childprocess (0.5.9)
+    childprocess (0.9.0)
       ffi (~> 1.0, >= 1.0.11)
     concurrent-ruby (1.0.5)
     contracts (0.16.0)
@@ -42,44 +42,45 @@ GEM
       multi_json (>= 1.7.5, < 2.0)
       multi_test (>= 0.1.2)
     diff-lcs (1.3)
-    docile (1.1.5)
-    ffi (1.9.18)
+    docile (1.3.1)
+    ffi (1.9.25)
     gherkin (2.12.2)
       multi_json (~> 1.3)
-    i18n (0.8.6)
+    i18n (1.1.0)
+      concurrent-ruby (~> 1.0)
     json (2.1.0)
-    minitest (5.10.3)
-    multi_json (1.12.2)
+    minitest (5.11.3)
+    multi_json (1.13.1)
     multi_test (0.1.2)
-    rake (12.1.0)
-    rspec (3.6.0)
-      rspec-core (~> 3.6.0)
-      rspec-expectations (~> 3.6.0)
-      rspec-mocks (~> 3.6.0)
-    rspec-core (3.6.0)
-      rspec-support (~> 3.6.0)
-    rspec-expectations (3.6.0)
+    rake (12.3.1)
+    rspec (3.8.0)
+      rspec-core (~> 3.8.0)
+      rspec-expectations (~> 3.8.0)
+      rspec-mocks (~> 3.8.0)
+    rspec-core (3.8.0)
+      rspec-support (~> 3.8.0)
+    rspec-expectations (3.8.1)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.6.0)
+      rspec-support (~> 3.8.0)
     rspec-its (1.2.0)
       rspec-core (>= 3.0.0)
       rspec-expectations (>= 3.0.0)
-    rspec-mocks (3.6.0)
+    rspec-mocks (3.8.0)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.6.0)
-    rspec-support (3.6.0)
-    simplecov (0.15.1)
-      docile (~> 1.1.0)
+      rspec-support (~> 3.8.0)
+    rspec-support (3.8.0)
+    simplecov (0.16.1)
+      docile (~> 1.1)
       json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.2)
     sqlite3 (1.3.13)
     thor (0.20.0)
     thread_safe (0.3.6)
     timecop (0.9.1)
-    tzinfo (1.2.3)
+    tzinfo (1.2.5)
       thread_safe (~> 0.1)
-    yard (0.9.12)
+    yard (0.9.16)
 
 PLATFORMS
   ruby
@@ -100,4 +101,4 @@ DEPENDENCIES
   yard
 
 BUNDLED WITH
-   1.16.1
+   1.16.3