Add missing cordova-browser engine (#888)

www/docs/en/dev/plugin_ref/spec.md

@@ -55,7 +55,7 @@ The child elements of the `<engines>` element specify versions of Apache Cordova
 
 Attributes(type) <br/> <span class="sub-header">Only for platform:</span> | Description
 ---------------- | ------------
-name(string) | *Required* <br/> Name of the engine. Here are the default engines that are supported : <ul><li> `cordova` </li> <li> `cordova-plugman` </li> <li> `cordova-android` </li> <li> `cordova-ios` </li> <li> `cordova-windows` </li> <li> `cordova-osx` </li> <li> `windows-os` </li> <li> `android-sdk` (returns the highest Android api level installed) </li> <li> `windows-sdk` (returns the native windows SDK version) </li> <li> `apple-xcode` (returns the xcode version) </li> <li> `apple-ios` (returns the highest iOS version installed) </li> <li> `apple-osx` (returns the OSX version) </li> You can also specify a custom framework apart from the default ones.
+name(string) | *Required* <br/> Name of the engine. Here are the default engines that are supported : <ul><li> `cordova` </li> <li> `cordova-plugman` </li> <li> `cordova-android` </li> <li> `cordova-browser` </li> <li> `cordova-ios` </li> <li> `cordova-windows` </li> <li> `cordova-osx` </li> <li> `windows-os` </li> <li> `android-sdk` (returns the highest Android api level installed) </li> <li> `windows-sdk` (returns the native windows SDK version) </li> <li> `apple-xcode` (returns the xcode version) </li> <li> `apple-ios` (returns the highest iOS version installed) </li> <li> `apple-osx` (returns the OSX version) </li> You can also specify a custom framework apart from the default ones.
 version(string) | *Required* <br/> The version that your framework must have in order to install. Semver syntax is supported.
 scriptSrc(string) | **For custom frameworks only** <br/> *Required* <br/>  The script file that tells plugman the version of the custom framework. Ideally, this file should be within the top level directory of your plugin directory.
 platform(string) | **For custom frameworks only** <br/> *Required* <br/> The platforms your framework supports. You may use the wildcard `*` to say supported for all platforms, specify multiple with a pipe character like `android|ios` or just a single platform like `android`.