Add specific slf4j-api version dependency

When just importing the ftp example as a maven project, I ran into the issue of a slf4j version discrepancy described here:
http://www.slf4j.org/faq.html#IllegalAccessError

This is solved by adding the specific version dependency of `slf4j-api`.

* Add the specific `slf4j-api` dependency to the Gradle script
* Change the dependency scope for `slf4j-` impl to the `runtime`.
* Regenerate POMs

basic/web-sockets/pom.xml

@@ -4,7 +4,7 @@
   <parent>
     <groupId>org.springframework.boot</groupId>
     <artifactId>spring-boot-starter-parent</artifactId>
-    <version>1.3.0.M5</version>
+    <version>1.3.0.RELEASE</version>
   </parent>
   <groupId>org.springframework.integration.samples</groupId>
   <artifactId>web-sockets</artifactId>
@@ -87,7 +87,7 @@
     <dependency>
       <groupId>org.springframework</groupId>
       <artifactId>spring-test</artifactId>
-      <version>4.2.0.RELEASE</version>
+      <version>4.2.3.RELEASE</version>
       <scope>test</scope>
     </dependency>
     <dependency>