Arc commands don't get whitespace trimmed

Most path commands are intelligently stripped so negative numbers, for instance, are not redundantly preceded by whitespace, but not arcs:

Example svg (the Twitter logo) that scour doesn't touch:

```
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 335 276" fill="#3ba9ee">
  <path d="m302 70a195 195 0 0 1 -299 175 142 142 0 0 0 97 -30 70 70 0 0 1 -58 -47 70 70 0 0 0 31 -2 70 70 0 0 1 -57 -66 70 70 0 0 0 28 5 70 70 0 0 1 -18 -90 195 195 0 0 0 141 72 67 67 0 0 1 116 -62 1
 </svg>
```

Shorter version:

```
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 335 276" fill="#3ba9ee">
  <path d="m302 70a195 195 0 0 1-299 175 142 142 0 0 0 97-30 70 70 0 0 1-58-47 70 70 0 0 0 31-2 70 70 0 0 1-57-66 70 70 0 0 0 28 5 70 70 0 0 1-18-90 195 195 0 0 0 141 72 67 67 0 0 1 116-62 117 117 0 0
 </svg>
```