Merge PR #402: Update noop-api module to follow style guide

Author: trask

noop-api/src/main/java/io/opentelemetry/contrib/noopapi/NoopContextStorageProvider.java

@@ -15,7 +15,7 @@
 /**
  * A {@link ContextStorageProvider} that returns a {@link ContextStorage} which is completely no-op.
  */
-public class NoopContextStorageProvider implements ContextStorageProvider {
+public final class NoopContextStorageProvider implements ContextStorageProvider {
 
   /** Returns a no-op context storage. */
   @Override

noop-api/src/main/java/io/opentelemetry/contrib/noopapi/NoopOpenTelemetry.java

@@ -42,7 +42,7 @@
  * <p>The above will succeed both with the {@linkplain OpenTelemetry#noop() default implementation}
  * and this one, but with this implementation there will be no overhead at all.
  */
-public class NoopOpenTelemetry implements OpenTelemetry {
+public final class NoopOpenTelemetry implements OpenTelemetry {
 
   private static final OpenTelemetry INSTANCE = new NoopOpenTelemetry();