Fixed versions in gradle files

app/build.gradle

 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 26
+    compileSdkVersion 27
     defaultConfig {
         applicationId "com.example.paktalin.lavina"
         minSdkVersion 15
-        targetSdkVersion 26
+        targetSdkVersion 27
         versionCode 1
         versionName "1.0"
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
@@ -20,7 +20,7 @@ android {
 
 dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
-    implementation 'com.android.support:appcompat-v7:26.1.0'
+    implementation 'com.android.support:appcompat-v7:27.1.1'
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'com.android.support.test:runner:1.0.2'
     androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'