test_sampler.cpp: typo in comment (2 invocation --> 2 invocations)

tests/sampler/test_sampler.cpp

@@ -11,7 +11,7 @@ struct Tester {
   explicit Tester(const execution_space& space) {
     //! Explicitly launch a kernel with a name, and run it 150 times with kernel
     //! logger. Use a periodic sampling with skip rate 51. This should print
-    //! out 2 invocation, and there is a single matcher with a regular
+    //! out 2 invocations, and there is a single matcher with a regular
     //! expression to check this.
 
     for (int iter = 0; iter < 150; iter++) {