update to stable toolchain (#122)

* update to stable toolchain

* remove toolchan note from routeguide

tonic-examples/helloworld-tutorial.md

@@ -21,17 +21,14 @@ $ cargo new helloworld-tonic
 $ cd helloworld-tonic
 ```
 
-`tonic` currently only works on rust `1.39-beta` and above as it requires support for the `async_await`
-feature. To install the beta simply follow the commands below:
+`tonic` works on rust `1.39` and above as it requires support for the `async_await`
+feature.
 
 ```bash
-$ rustup install beta
-$ rustup component add rustfmt --toolchain beta
-$ rustup default beta
+$ rustup update
+$ rustup component add rustfmt
 ```
 
-We recommend setting `rustup default` to `beta` as this is the version tools like RLS and rust-analyzer will use to watch your code, and could degrade your experience when developing using Tonic as they will not be able to provide support.
-
 ## Defining the HelloWorld service
 
 Our first step is to define the gRPC _service_ and the method _request_ and _response_ types using

tonic-examples/routeguide-tutorial.md

@@ -53,10 +53,6 @@ Tonic uses `rustfmt` to tidy up the code it generates, so we'll make sure it's i
 $ rustup component add rustfmt
 ```
 
-**Note** Prior to rust's 1.39 release, Tonic may be pinned to a specific toolchain version. Running
-the above command may first download and install a different toolchain. Check the project's [readme]
-for the latest requirements.
-
 Run the server
 ```shell
 $ cargo run --bin routeguide-server