Apply modernize-use-nullptr

Setup:
- `mkdir tidy; cd tidy`
- `cmake .. -DCMAKE_BUILD_TYPE=debug -DPROC_TARGET_NUMBER=1 -DCACHE_NAME_SUFFIX=4 -DBINDIR=. -DDATADIR=. -DBUILD_BUNDLE=ON -DWITH_LTO=OFF -DOPTION_OMP=OFF -DCMAKE_EXPORT_COMPILE_COMMANDS=ON`
- `cd ..`
- `find -name '*.cc' -exec clang-tidy-3.8 -header-filter=.* -p=tidy -fix-errors -checks=modernize-use-nullptr {} \;`

rtgui/coordinateadjuster.h

@@ -47,7 +47,7 @@ class CoordinateProvider
 protected:
     CoordinateAdjuster *coordinateAdjuster;
 public:
-    CoordinateProvider() : coordinateAdjuster(NULL) {}
+    CoordinateProvider() : coordinateAdjuster(nullptr) {}
     virtual ~CoordinateProvider() {}
     void setListener(CoordinateAdjuster *adjuster)
     {