Fix typo in README.md

README.md

@@ -24,7 +24,7 @@
 - **Intuitive**: Profiler can be started/stopped and results can be obtained from any time and any thread.
 - **Standards Compliant**: Profiler results can be saved in [callgrind](http://valgrind.org/docs/manual/cl-format.html) or [pstat](http://docs.python.org/3.4/library/profile.html#pstats.Stats) formats.
 - **Rich in Feature set**: Profiler results can show either [Wall Time](https://en.wikipedia.org/wiki/Elapsed_real_time) or actual [CPU Time](http://en.wikipedia.org/wiki/CPU_time) and can be aggregated from different sessions. Various flags are defined for filtering and sorting profiler results.
-- **Robust**: Yappi had been around for years.
+- **Robust**: Yappi has been around for years.
 
 ## Motivation