Add newline to end of files missing a newline (#4979)

This is to get rid of the "No newline at end of file" warning.

Author: benjchristensen

DESIGN.md

@@ -40,4 +40,4 @@
     <property name="fileExtensions" value=".java"/>
   </module>
    -->
-</module>
+</module>

checkstyle.xml

@@ -56,4 +56,4 @@ public interface CompletableEmitter {
      * @return true if the downstream disposed the sequence
      */
     boolean isDisposed();
-}
+}

src/main/java/io/reactivex/CompletableEmitter.java

@@ -63,4 +63,4 @@ public interface FlowableEmitter<T> extends Emitter<T> {
      * @return the serialized FlowableEmitter
      */
     FlowableEmitter<T> serialize();
-}
+}

src/main/java/io/reactivex/FlowableEmitter.java

@@ -64,4 +64,4 @@ public interface MaybeEmitter<T> {
      * @return true if the downstream cancelled the sequence
      */
     boolean isDisposed();
-}
+}

src/main/java/io/reactivex/MaybeEmitter.java

@@ -27,4 +27,4 @@ public interface ObservableSource<T> {
      * @throws NullPointerException if {@code observer} is null
      */
     void subscribe(Observer<? super T> observer);
-}
+}

src/main/java/io/reactivex/ObservableSource.java

@@ -73,4 +73,4 @@ public interface Observer<T> {
      */
     void onComplete();
 
-}
+}

src/main/java/io/reactivex/Observer.java

@@ -59,4 +59,4 @@ public interface SingleEmitter<T> {
      * @return true if the downstream cancelled the sequence
      */
     boolean isDisposed();
-}
+}

src/main/java/io/reactivex/SingleEmitter.java

@@ -17,4 +17,4 @@
 /**
  * Annotations for indicating experimental and beta operators, classes, methods, types or fields.
  */
-package io.reactivex.annotations;
+package io.reactivex.annotations;

src/main/java/io/reactivex/annotations/package-info.java

@@ -19,4 +19,4 @@
  * (Disposable container types) and utility classes to construct
  * Disposables from callbacks and other types.
  */
-package io.reactivex.disposables;
+package io.reactivex.disposables;