use parent/child constructor instead of string concat

Author: littleaj

core/src/main/java/com/microsoft/applicationinsights/extensibility/initializer/docker/internal/DockerContextPoller.java

@@ -41,7 +41,7 @@ protected DockerContextPoller(File contextFile, DockerContextFactory dockerConte
     }
 
     public DockerContextPoller(String contextFileDirectory) {
-        this(new File(contextFileDirectory + "/" + CONTEXT_FILE_NAME), new DockerContextFactory());
+        this(new File(contextFileDirectory, CONTEXT_FILE_NAME), new DockerContextFactory());
         this.setDaemon(true);
         this.setName(DockerContextPoller.class.getSimpleName());
     }