fix typo in README.md

README.md

@@ -108,7 +108,7 @@ that should be compatible with this version:
 * [Iris Atomic](https://gitlab.mpi-sws.org/iris/atomic) is an experimental
   formalization of logically atomic triples in Iris.
 * [Iron](https://gitlab.mpi-sws.org/iris/iron) is a linear separation logic
-  build on top of Iris for precise reasoning about resources (such as making
+  built on top of Iris for precise reasoning about resources (such as making
   sure there are no memory leaks).
 
 ## Further Resources