Update PowershellSyntax.tmLanguage

Fixes several issues:
**229**: Correctly highlights the operators ```-clt```, ```-cle```, ```-cgt```, ```-cge```
**235**: Fixes issues highlighting paths with symbols in them
**259** & **265**: Fixes issues with operator highlighting, such as ```-NoTypeInformation``` being incorrectly highlighted as two elements, but allows for ```-Not1``` to be correctly interpreted as two elements
**393**: Allows for permissible symbols in command names
```?!\p{L}``` is anything that is not a letter. This correctly allows for -not1, but does not highlight ```-NoTypeInformation```.