Downgrade simplecov

SimpleCov 0.18 is incompatible with the Code Climate reporter

For more info:
codeclimate/test-reporter#413

Gemfile.lock

@@ -57,6 +57,7 @@ GEM
       concurrent-ruby (~> 1.0)
     ice_nine (0.11.2)
     jaro_winkler (1.5.3)
+    json (2.3.0)
     kwalify (0.7.2)
     listen (3.2.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
@@ -112,10 +113,11 @@ GEM
       rubocop (>= 0.68.1)
     ruby-progressbar (1.10.1)
     shellany (0.0.1)
-    simplecov (0.18.5)
+    simplecov (0.17.1)
       docile (~> 1.1)
-      simplecov-html (~> 0.11)
-    simplecov-html (0.12.2)
+      json (>= 1.8, < 3)
+      simplecov-html (~> 0.10.0)
+    simplecov-html (0.10.2)
     sqlite3 (1.4.1)
     thor (0.20.3)
     thread_safe (0.3.6)
@@ -144,7 +146,7 @@ DEPENDENCIES
   rubocop (~> 0.72.0)
   rubocop-performance (~> 1.5)
   rubocop-rspec (~> 1.36)
-  simplecov (~> 0.18.5)
+  simplecov (~> 0.17.1)
   sqlite3 (~> 1.4)
 
 BUNDLED WITH

human_enum.gemspec

@@ -31,7 +31,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'bundler', '~> 2.0'
   spec.add_development_dependency 'rake', '~> 13.0'
   spec.add_development_dependency 'rspec', '~> 3.0'
-  spec.add_development_dependency 'simplecov', '~> 0.18.5'
+  spec.add_development_dependency 'simplecov', '~> 0.17.1'
 
   spec.add_development_dependency 'rubocop', '~> 0.72.0'
   spec.add_development_dependency 'rubocop-performance', '~> 1.5'