Fixed some typos in errors

ref #76

src/errors/ScanStationErrors.ts

@@ -2,7 +2,7 @@ import { IsString } from 'class-validator';
 import { NotAcceptableError, NotFoundError } from 'routing-controllers';
 
 /**
- * Error to throw, when a non-existant scan station get's loaded.
+ * Error to throw, when a non-existent scan station get's loaded.
  */
 export class ScanStationNotFoundError extends NotFoundError {
 	@IsString()