Added ios platform version restrictions (#158)

diff --git a/README.md b/README.md
index e6bf628..06ba3d0 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@
 Installation
 -----------
 
-This plugin needs cordova-ios >4.0.0.
+This plugin needs cordova-ios 4.0.0 - 5.x. This plugin is not supported on cordova-ios >6.0.0.
 
 To install the current release:
 
diff --git a/package.json b/package.json
index e8c20d8..b8e098f 100644
--- a/package.json
+++ b/package.json
@@ -27,7 +27,8 @@
   "engines": {
     "cordovaDependencies": {
       "2.0.0": {
-        "cordova": ">100"
+        "cordova": ">100",
+        "cordova-ios": "<6.0.0"
       }
     }
   },
diff --git a/plugin.xml b/plugin.xml
index d4af280..9c7bb48 100644
--- a/plugin.xml
+++ b/plugin.xml
@@ -30,7 +30,7 @@
     <repo>https://github.com/apache/cordova-plugin-wkwebview-engine</repo>
 
 	<engines>
-        <engine name="cordova-ios" version=">=4.0.0-dev" />
+        <engine name="cordova-ios" version=">=4.0.0 <6.0.0" />
         <engine name="apple-ios" version=">=9.0" />
 	</engines>
 
diff --git a/tests/ios/package.json b/tests/ios/package.json
index 1292141..67cdf81 100644
--- a/tests/ios/package.json
+++ b/tests/ios/package.json
@@ -5,7 +5,7 @@
     "author": "Apache Software Foundation",
     "license": "Apache-2.0",
     "dependencies": {
-        "cordova-ios": "*"
+        "cordova-ios": "^5.1.1"
     },
     "scripts": {
         "test": "xcodebuild test -workspace CDVWKWebViewEngineTest.xcworkspace -scheme CDVWKWebViewEngineLibTests -destination 'platform=iOS Simulator,name=iPhone 5' -xcconfig test.xcconfig"