Fix a hidden dependency on the old V1 plugin API

TopsyTurvy derived from `KaleidoscopePlugin`, which was part of the V1 plugin
API, and has been recently removed. Use `kaleidoscope::Plugin` instead, which is
its replacement.

Signed-off-by: Gergely Nagy <algernon@keyboard.io>

src/Kaleidoscope/TopsyTurvy.h

@@ -25,7 +25,7 @@
 
 namespace kaleidoscope {
 
-class TopsyTurvy: public KaleidoscopePlugin {
+class TopsyTurvy: public kaleidoscope::Plugin {
  public:
   TopsyTurvy(void) {}