travi: typo fix

.travis.yml

@@ -25,7 +25,7 @@ matrix:
 install:
   - rustup target add wasm32-unknown-unknown --toolchain nightly
   # travis installs rust using rustup with the "minimal" profile so these tools are not installed by default
-  - rustup component add rustfmt --tolchain nightly
+  - rustup component add rustfmt --toolchain nightly
   # choosing to add clippy for the nightly toolchain only
   # becuase we want to run it with nighly to avoid having to set BUILD_DUMMY_WASM_BINARY=0
   # setting that variable requires changing it in a later run of cargo bulid to ensure runtime/build.rs