message: Fix a typo in contributing guidelines
diff: @@ -195,7 +195,7 @@ General
  - Never declare more than one variable per line.
  - Only separate functions with vertical whitespaces and use comments to
  - document logcial blocks inside functions.
  + document logical blocks inside functions.
  - Use `.hpp` as suffix for header files and `.cpp` as suffix for implementation
  files.
  