Update contributing

Author: 38

.github/workflows/push-check.yml

@@ -16,7 +16,7 @@ jobs:
     - uses: actions-rs/cargo@v1
       with:
           command: test
-          args: --verbose --all-features
+          args: --verbose
   build_and_test:
     runs-on: ${{ matrix.os }}
     strategy:

CONTRIBUTING.md

@@ -108,7 +108,7 @@ For the debugging you could set the `NO_HEADLESS=1` environment variable to run
 ### Minimal Supported Compiler Version
 
 Currently we should make sure Plotters is compatible with rustc 1.36.0.
-Before making a PR, please check if the code compile with 1.36.0
+Before making a PR, please check if the code compile with 1.36.0 (with default features).
 
 ### Code Coverage