2.x: Fix Javadoc warnings, links to the JDK types (#5861)

Author: akarnokd

build.gradle

@@ -91,8 +91,10 @@ javadoc {
     options.addStringOption("doctitle").value = ""
     options.addStringOption("header").value = ""
 
-    options.links("http://docs.oracle.com/javase/7/docs/api/")
-    options.links("http://www.reactive-streams.org/reactive-streams-${reactiveStreamsVersion}-javadoc/")
+    options.links(
+        "https://docs.oracle.com/javase/7/docs/api/",
+        "http://www.reactive-streams.org/reactive-streams-${reactiveStreamsVersion}-javadoc/"
+    )
 
     if (JavaVersion.current().isJava7()) {
         // "./gradle/stylesheet.css" only supports Java 7

src/main/java/io/reactivex/CompletableObserver.java

@@ -28,7 +28,6 @@
  * Calling the {@code CompletableObserver}'s method must happen in a serialized fashion, that is, they must not
  * be invoked concurrently by multiple threads in an overlapping fashion and the invocation pattern must
  * adhere to the following protocol:
- * <p>
  * <pre><code>    onSubscribe (onError | onComplete)?</code></pre>
  * <p>
  * Subscribing a {@code CompletableObserver} to multiple {@code CompletableSource}s is not recommended. If such reuse

src/main/java/io/reactivex/MaybeObserver.java

@@ -28,7 +28,6 @@
  * Calling the {@code MaybeObserver}'s method must happen in a serialized fashion, that is, they must not
  * be invoked concurrently by multiple threads in an overlapping fashion and the invocation pattern must
  * adhere to the following protocol:
- * <p>
  * <pre><code>    onSubscribe (onSuccess | onError | onComplete)?</code></pre>
  * <p>
  * Note that unlike with the {@code Observable} protocol, {@link #onComplete()} is not called after the success item has been

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

@@ -30,7 +30,6 @@
  * Calling the {@code Observer}'s method must happen in a serialized fashion, that is, they must not
  * be invoked concurrently by multiple threads in an overlapping fashion and the invocation pattern must
  * adhere to the following protocol:
- * <p>
  * <pre><code>    onSubscribe onNext* (onError | onComplete)?</code></pre>
  * <p>
  * Subscribing an {@code Observer} to multiple {@code ObservableSource}s is not recommended. If such reuse

src/main/java/io/reactivex/SingleObserver.java

@@ -28,7 +28,6 @@
  * Calling the {@code SingleObserver}'s method must happen in a serialized fashion, that is, they must not
  * be invoked concurrently by multiple threads in an overlapping fashion and the invocation pattern must
  * adhere to the following protocol:
- * <p>
  * <pre><code>    onSubscribe (onSuccess | onError)?</code></pre>
  * <p>
  * Subscribing a {@code SingleObserver} to multiple {@code SingleSource}s is not recommended. If such reuse