Rename appengine.version to avoid clash with Appe Engine's Maven plugin

Closes gh-7433

spring-boot-dependencies/pom.xml

@@ -45,7 +45,7 @@
 	<properties>
 		<activemq.version>5.13.4</activemq.version>
 		<antlr2.version>2.7.7</antlr2.version>
-		<appengine.version>1.9.44</appengine.version>
+		<appengine-sdk.version>1.9.44</appengine-sdk.version>
 		<artemis.version>1.5.0</artemis.version>
 		<aspectj.version>1.8.9</aspectj.version>
 		<assertj.version>2.5.0</assertj.version>
@@ -702,7 +702,7 @@
 			<dependency>
 				<groupId>com.google.appengine</groupId>
 				<artifactId>appengine-api-1.0-sdk</artifactId>
-				<version>${appengine.version}</version>
+				<version>${appengine-sdk.version}</version>
 			</dependency>
 			<dependency>
 				<groupId>com.google.code.gson</groupId>