Upraded capybara and poltergeist gems; Add puma gem

Gemfile.lock

@@ -62,13 +62,13 @@ GEM
     bundler-audit (0.6.0)
       bundler (~> 1.2)
       thor (~> 0.18)
-    capybara (2.18.0)
+    capybara (3.0.3)
       addressable
       mini_mime (>= 0.1.3)
-      nokogiri (>= 1.3.3)
-      rack (>= 1.0.0)
-      rack-test (>= 0.5.4)
-      xpath (>= 2.0, < 4.0)
+      nokogiri (~> 1.8)
+      rack (>= 1.6.0)
+      rack-test (>= 0.6.3)
+      xpath (~> 3.0)
     childprocess (0.9.0)
       ffi (~> 1.0, >= 1.0.11)
     cliver (0.3.2)
@@ -184,8 +184,8 @@ GEM
     parallel (1.12.1)
     parser (2.5.1.0)
       ast (~> 2.4.0)
-    poltergeist (1.17.0)
-      capybara (~> 2.1)
+    poltergeist (1.18.0)
+      capybara (>= 2.1, < 4)
       cliver (~> 0.3.1)
       websocket-driver (>= 0.2.0)
     powder (0.4.0)
@@ -198,6 +198,7 @@ GEM
     pry-rails (0.3.6)
       pry (>= 0.10.4)
     public_suffix (3.0.2)
+    puma (3.11.4)
     rack (2.0.5)
     rack-livereload (0.3.17)
       rack
@@ -350,6 +351,7 @@ DEPENDENCIES
   powder
   pry
   pry-rails
+  puma
   rack-livereload
   rails (= 5.1.6)
   rails-perftest