#230: Fix Javadoc punctuation.

Author: heshamMassoud

src/main/java/com/commercetools/sync/services/ProductService.java

@@ -17,7 +17,7 @@ public interface ProductService {
 
     /**
      * Given a {@code key}, if it is blank (null/empty), a completed future with an empty optional is returned.
-     * This method then checks if the cached map of product keys -> ids contains the key, if it does, then an
+     * This method then checks if the cached map of product keys -> ids contains the key. If it does, then an
      * optional containing the mapped id is returned. If the cache doesn't contain the key; this method attempts to
      * fetch the id of the key from the CTP project, caches it and returns a
      * {@link CompletionStage}<{@link Optional}<{@link String}>> in which the result of it's completion