Update gradle wrapper and build-tools version for flutter create. (#8914)

* Update gradle wrapper and build-tools version.

Tested manually by "flutter create" with Idea "flutter run" and from android studio "run" android app.

* Update com.android.tools.build to 2.3.0

packages/flutter_tools/gradle/flutter.gradle

@@ -21,7 +21,7 @@ buildscript {
     jcenter()
   }
   dependencies {
-    classpath 'com.android.tools.build:gradle:2.2.3'
+    classpath 'com.android.tools.build:gradle:2.3.0'
   }
 }
 

packages/flutter_tools/templates/create/android.tmpl/build.gradle

@@ -4,7 +4,7 @@ buildscript {
     }
 
     dependencies {
-        classpath 'com.android.tools.build:gradle:2.2.3'
+        classpath 'com.android.tools.build:gradle:2.3.0'
     }
 }
 
@@ -24,5 +24,5 @@ task clean(type: Delete) {
 }
 
 task wrapper(type: Wrapper) {
-    gradleVersion = '2.14.1'
+    gradleVersion = '3.4.1'
 }