Use containing Android sdk and build tools version numbers (#45)

* Update build.gradle to read from containing project

* Create index.d.ts

* Remove new line for consistency with upstream

Author: asutula

android/build.gradle

@@ -1,21 +1,17 @@
 
 apply plugin: 'com.android.library'
 
-def _ext = rootProject.ext
-
-def _compileSdkVersion = _ext.has('compileSdkVersion') ? _ext.compileSdkVersion : 23
-def _buildToolsVersion = _ext.has('buildToolsVersion') ? _ext.buildToolsVersion : '23.0.1'
-def _minSdkVersion = _ext.has('minSdkVersion') ? _ext.minSdkVersion : 16
-def _targetSdkVersion = _ext.has('targetSdkVersion') ? _ext.targetSdkVersion : 22
-
+def DEFAULT_COMPILE_SDK_VERSION = 27
+def DEFAULT_BUILD_TOOLS_VERSION = "27.0.3"
+def DEFAULT_TARGET_SDK_VERSION = 27
 
 android {
-    compileSdkVersion _compileSdkVersion
-    buildToolsVersion _buildToolsVersion
+    compileSdkVersion project.hasProperty('compileSdkVersion') ? project.compileSdkVersion : DEFAULT_COMPILE_SDK_VERSION
+    buildToolsVersion project.hasProperty('buildToolsVersion') ? project.buildToolsVersion : DEFAULT_BUILD_TOOLS_VERSION
 
     defaultConfig {
-        minSdkVersion _minSdkVersion
-        targetSdkVersion _targetSdkVersion
+        minSdkVersion 16
+        targetSdkVersion project.hasProperty('targetSdkVersion') ? project.targetSdkVersion : DEFAULT_TARGET_SDK_VERSION
         versionCode 1
         versionName "1.0"
         ndk {
@@ -30,4 +26,4 @@ android {
 dependencies {
     compile 'com.facebook.react:react-native:+'
 }
-  
+