message: Mark mlir code snippets as being written in mlir
  Forgot to add these in previous change :/
diff: @@ -209,7 +209,7 @@ test the dependence analysis infra in the code generator, Andy Davis wrote a
  simple pass that checks dependencies and emits them as "notes", allowing him to
  write tests like this:
  -``` {.mlir}
  +```mlir {.mlir}
  // RUN: mlir-opt %s -memref-dependence-check -verify
  mlfunc @different_memrefs() {
  %m.a = alloc() : memref<100xf32>
  @@ -243,7 +243,7 @@ with ShapeRefiner.
  The [MLIR Tensor Type](g3doc/LangRef.md#tensor-type) directly captures shape
  information, so you can have things like:
  -``` {.mlir}
  +```mlir {.mlir}
  %x = tf.Add %x, %y : tensor<128 x 8 x ? x f32>
  ```
  