Don't use 0 as null pointer constant.

src/Query.cpp

@@ -63,7 +63,7 @@ void Query::end() {
 
     glEndQuery(static_cast<GLenum>(*target));
     delete target;
-    target = 0;
+    target = nullptr;
 }
 
 void SampleQuery::begin(SampleQuery::Target target) {
@@ -76,7 +76,7 @@ void SampleQuery::end() {
 
     glEndQuery(static_cast<GLenum>(*target));
     delete target;
-    target = 0;
+    target = nullptr;
 }
 
 }