add javax.annotation-api dependency to xxl-job-core/pom.xml

The class com.xxl.job.core.glue.impl.SpringGlueFactory imports
javax.annotation.Resource, which requires the annotation API.  This commit
adds this dependency to the Maven build.

xxl-job-core/pom.xml

@@ -45,6 +45,13 @@
 			<scope>test</scope>
 		</dependency>
 
+		<!-- javax.annotation -->
+		<dependency>
+			<groupId>javax.annotation</groupId>
+			<artifactId>javax.annotation-api</artifactId>
+			<version>1.3.2</version>
+		</dependency>
+
 	</dependencies>
 
 </project>