[docs, ci] update cargo-contract installation (#371)

.gitlab-ci.yml

@@ -148,7 +148,7 @@ fmt:
 
 .update-cargo-contract:            &update-cargo-contract
   # `cargo install` returns an error if there is nothing to update, so have to supress it here temporarily
-  - cargo install --git https://github.com/paritytech/cargo-contract || echo $?
+  - cargo install cargo-contract || echo $?
   - cargo contract -V
 
 examples-test:

README.md

@@ -45,7 +45,7 @@ Use the scripts provided under `scripts` directory in order to run checks on eit
 For building the example smart contracts found under `examples` you will need to have [`cargo-contract`](https://github.com/paritytech/cargo-contract) installed.
 
 ```
-cargo install --git https://github.com/paritytech/cargo-contract cargo-contract --force
+cargo install cargo-contract --force
 ```
 
 Use the `--force` to ensure you are updated to the most recent `cargo-contract` version.

examples/README.md

@@ -9,7 +9,7 @@ Have a look at the different examples to better understand how to use ink! to bu
 For building the example smart contracts found in this folder you will need to have [`cargo-contract`](https://github.com/paritytech/cargo-contract) installed.
 
 ```
-cargo install --force --git https://github.com/paritytech/ink cargo-contract
+cargo install cargo-contract --force
 ```
 
 We use the `--force` to update to the most recent `cargo-contract` version.