Add overmind as the first option to run

Changes:
- Use Ruby instead of bash script for cross-platform use
- Prefer Overmind over Foreman
- Show relevant messages if both Overmind and Foreman not installed
  and if Procfile missing

lib/generators/react_on_rails/bin/dev

@@ -1,9 +1,32 @@
-#!/usr/bin/env bash
+#!/usr/bin/env ruby
+# frozen_string_literal: true
 
-if ! command -v foreman &> /dev/null
-then
-  echo "Installing foreman…"
-  gem install foreman && echo "Foreman Installed."
-fi
+def installed?(process)
+  IO.popen "#{process} -v"
+rescue Errno::ENOENT
+  false
+end
 
-foreman start -f Procfile.dev
+def run(process)
+  argv = ARGV.join(" ")
+  puts "Using #{process}"
+  exec "#{process} start -f Procfile.dev", argv
+rescue Errno::ENOENT
+  puts <<~MSG
+    ERROR:
+    Please ensure `Procfile.dev` exist in your project!
+  MSG
+  exit!
+end
+
+if installed? "overmind"
+  run "overmind"
+elsif installed? "foreman"
+  run "foreman"
+else
+  puts <<~MSG
+    NOTICE:
+    For this script to run, you need either 'overmind' or 'foreman' installed on your machine. Please try this script after installing one of them.
+  MSG
+  exit!
+end

lib/generators/react_on_rails/bin/dev-static

@@ -1,9 +1,32 @@
-#!/usr/bin/env bash
+#!/usr/bin/env ruby
+# frozen_string_literal: true
 
-if ! command -v foreman &> /dev/null
-then
-  echo "Installing foreman…"
-  gem install foreman && echo "Foreman Installed."
-fi
+def installed?(process)
+  IO.popen "#{process} -v"
+rescue Errno::ENOENT
+  false
+end
 
-foreman start -f Procfile.dev-static
+def run(process)
+  argv = ARGV.join(" ")
+  puts "Using #{process}"
+  exec "#{process} start -f Procfile.dev-static", argv
+rescue Errno::ENOENT
+  puts <<~MSG
+    ERROR:
+    Please ensure `Procfile.dev-static` exist in your project!
+  MSG
+  exit!
+end
+
+if installed? "overmind"
+  run "overmind"
+elsif installed? "foreman"
+  run "foreman"
+else
+  puts <<~MSG
+    NOTICE:
+    For this script to run, you need either 'overmind' or 'foreman' installed on your machine. Please try this script after installing one of them.
+  MSG
+  exit!
+end