Qml: Consistently use nullptr

Fixed by clang-tidy modernize-use-nullptr.

Change-Id: Ibe0dddaacbabd47b5a0519ae361132818d5b8be2
Reviewed-by: Marco Benelli <marco.benelli@qt.io>

src/plugins/qmljstools/qmljssemanticinfo.h

@@ -44,7 +44,7 @@ namespace QmlJSTools {
 class QMLJSTOOLS_EXPORT Range
 {
 public:
-    Range(): ast(0) {}
+    Range(): ast(nullptr) {}
 
 public: // attributes
     QmlJS::AST::Node *ast;