[doc] Fix typo

CONTRIBUTING.md

@@ -10,4 +10,4 @@ Taichi is developed mainly in C++17 and Python3. Please check out the [Developer
 
 Issues marked with ["welcome contribution"](https://github.com/taichi-dev/taichi/issues?q=is%3Aopen+is%3Aissue+label%3A%22welcome+contribution%22) are great places for starters. You can quickly get an idea of the entire workflow and how to join the community.
 
-**RFC**: We use the `RFC` (Request for Comments) mechanism to discuss and organize some of the more advanced and self-contained features. These are the projects that we would like to work on but still lack a concrete design or implementation roadmap for because of their complexity. We document these requests and the threaded proposals in the hope that we could provide the community with a good enough context and draw upon insights from the potentially passionate minds. You can find all the ongoing RFCs [here](https://github.com/taichi-dev/taichi/issues?q=is%3Aissue+is%3Aopen+label%3ARFC+), and you are also welcome to file new RFCs with us!
+**RFC**: We use the `RFC` (Request for Comments) mechanism to discuss and organize some of the more advanced and self-contained features. These are the projects that we would like to work on but still lack a concrete design or implementation roadmap for their complexity. We document these requests and the threaded proposals in the hope that we could provide the community with a good enough context and draw upon insights from the potentially passionate minds. You can find all the ongoing RFCs [here](https://github.com/taichi-dev/taichi/issues?q=is%3Aissue+is%3Aopen+label%3ARFC+), and you are also welcome to file new RFCs with us!