parser: removed allocation by strings.TrimRight
parser: removed allocation by strings.TrimRight

```
benchmark                         old ns/op     new ns/op     delta
BenchmarkParseFromString001-4     2855          2710          -5.08%
BenchmarkParseFromStatus401-4     24.5          23.7          -3.27%
BenchmarkParseFromString002-4     304489        307000        +0.82%

benchmark                         old allocs     new allocs     delta
BenchmarkParseFromString001-4     14             13             -7.14%
BenchmarkParseFromStatus401-4     0              0              +0.00%
BenchmarkParseFromString002-4     1485           1485           +0.00%
```

temoto/robotstxt,temoto/robotstxt,temoto/robotstxt-go