maven.adoc: correct the levels of 2 section titles

docs/modules/ROOT/pages/getting-started/maven.adoc

@@ -43,7 +43,7 @@ For a basic Android application, you need at least:
 *  jme3-android
 *  jme3-android-native
 
-=== Gradle
+== Gradle
 
 [source,groovy]
 ----
@@ -59,7 +59,7 @@ dependencies {
 }
 ----
 
-=== Maven
+== Maven
 
 [source,xml]
 ----