replace assert.h with cassert

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/java/Class.hxx

@@ -33,7 +33,7 @@
 #include "Ref.hxx"
 #include "Exception.hxx"
 
-#include <assert.h>
+#include <cassert>
 
 namespace Java {
 	/**

src/java/Object.hxx

@@ -34,7 +34,7 @@
 
 #include <jni.h>
 
-#include <assert.h>
+#include <cassert>
 
 namespace Java {
 	/**

src/java/Ref.hxx

@@ -34,10 +34,9 @@
 
 #include <jni.h>
 
+#include <cassert>
 #include <utility>
 
-#include <assert.h>
-
 namespace Java {
 	/**
 	 * Hold a local reference on a JNI object.