Fix .gitignore pattern for Maven "target" folders

Rationale: changes in org.springframework.aop.framework.autoproxy.target
were previously ignored since the "target" package was ignored by the
previous "eager" pattern for "target" folders.

.gitignore

@@ -29,7 +29,7 @@ spring-test/test-output/
 
 # Maven artifacts
 pom.xml
-target/
+/target/
 
 # Eclipse artifacts, including WTP generated manifests
 bin