Fix typo in pull request template

Author: siriak

.github/pull_request_template.md

@@ -17,7 +17,7 @@ Please delete options that are not relevant.
 ## Checklist:
 
 - [ ] I ran bellow commands using the latest version of **rust nightly**.
-- [ ] I ran `cargo clippy --all -- -D warning` just before my last commit and fixed any issue that was found.
+- [ ] I ran `cargo clippy --all -- -D warnings` just before my last commit and fixed any issue that was found.
 - [ ] I ran `cargo fmt` just before my last commit.
 - [ ] I ran `cargo test` just before my last commit and all tests passed.
 - [ ] I checked `COUNTRIBUTING.md` and my code follows its guidelines.