Replace learnt with learned (apache#3684)

README.md

@@ -41,8 +41,8 @@ Checkout the [Contributor Guide](https://docs.tvm.ai/contribute/)
 
 Acknowledgement
 ---------------
-We learnt a lot from the following projects when building TVM.
+We learned a lot from the following projects when building TVM.
 - [Halide](https://github.com/halide/Halide): TVM uses [HalideIR](https://github.com/dmlc/HalideIR) as data structure for
-  arithmetic simplification and low level lowering. We also learnt and adapted some part of lowering pipeline from Halide.
+  arithmetic simplification and low level lowering. We also learned and adapted some part of lowering pipeline from Halide.
 - [Loopy](https://github.com/inducer/loopy): use of integer set analysis and its loop transformation primitives.
 - [Theano](https://github.com/Theano/Theano): the design inspiration of symbolic scan operator for recurrence.