fix(proposals): shell exec style

Executing file directly must start with (absolute/relative) path under Linux

docs/proposals.md

@@ -596,7 +596,7 @@ console.log(1);
 $ node hello.js
 
 # hashbang 的方式
-$ hello.js
+$ ./hello.js
 ```
 
 对于 JavaScript 引擎来说，会把`#!`理解成注释，忽略掉这一行。