Changed appcompat dependency to 26.1.0

 # 1.1.0
 * Rename classes to satisfy Dart conventions
 * Remove useless new and const keywords
+* Changed appcompat dependency to 26.1.0
 
 # 1.0.6
 * Add screenshot example

@@ -34,5 +34,5 @@ android {
 }
 
 dependencies {
-    api 'com.android.support:appcompat-v7:27.1.1'
+    api 'com.android.support:appcompat-v7:26.1.0'
 }