fix: replace strings.TrimLeft with strings.TrimPrefix

[knbr13]

strings.TrimLeft: TrimLeft returns a slice of the string s with all leading Unicode code points contained in cutset removed.
To remove a prefix, use [TrimPrefix] instead.

example:

s := "hello, world!"
s1 := strings.TrimLeft(s, "olhe,") // s1 = " world!"
s2 := strings.TrimPrefix(s, "hello,") // s2 = " world!"

in the original code, both of them work fine, but the intention of the original code is clearly to remove a prefix rather than all leading Unicode code points contained in cutset, using strings.TrimPrefix clarifies the writer's intention and adheres to the standard library's recommendation.