fix img url in css file, verstion to 0.1.5

lib/bootstrap_beagle/version.rb

 module BootstrapBeagle
 module BootstrapBeagle
-  VERSION = "0.1.4"
+  VERSION = "0.1.5"
 end
 end

vendor/assets/stylesheets/multiselect/css/multi-select.css

 .ms-container{
 .ms-container{
-  background: transparent url('../img/switch.png') no-repeat 50% 50%;
+  background: transparent url('/assets/img/switch.png') no-repeat 50% 50%;
   width: 370px;
   width: 370px;
 }
 }