Use Dict for type instead of dict (#262)

This change is to fix a bug as dict is not compatible with Python 3.8

src/shiv/__version__.py

@@ -1 +1 @@
-__version__ = "1.0.7"
+__version__ = "1.0.8"

src/shiv/bootstrap/environment.py

@@ -4,7 +4,7 @@
 """
 import json
 import os
-from typing import Any, Optional
+from typing import Any, Dict, Optional
 
 
 def str_bool(v) -> bool:
@@ -35,7 +35,7 @@ def __init__(
         entry_point: Optional[str] = None,
         extend_pythonpath: bool = False,
         prepend_pythonpath: Optional[str] = None,
-        hashes: Optional[dict[str, Any]] = None,
+        hashes: Optional[Dict[str, Any]] = None,
         no_modify: bool = False,
         reproducible: bool = False,
         script: Optional[str] = None,
@@ -46,7 +46,7 @@ def __init__(
         self.always_write_cache: bool = always_write_cache
         self.build_id: Optional[str] = build_id
         self.built_at: str = built_at
-        self.hashes: Optional[dict[str, Any]] = hashes or {}
+        self.hashes: Optional[Dict[str, Any]] = hashes or {}
         self.no_modify: bool = no_modify
         self.reproducible: bool = reproducible
         self.preamble: Optional[str] = preamble