Correcting format

In my haste to submit a pull-request I neglected to check format. Apologies.

maturin/__main__.py

@@ -4,35 +4,39 @@
 import sysconfig
 from typing import Optional
 
+
 def get_maturin_path() -> Optional[Path]:
     SCRIPT_NAME = "maturin"
 
     def script_dir(scheme: str) -> Path:
         return sysconfig.get_path("scripts", scheme)
-    
+
     def script_exists(dir: Path) -> bool:
         for _, _, files in os.walk(dir):
             for f in files:
                 name, *_ = os.path.splitext(f)
                 if name == SCRIPT_NAME:
                     return True
-        
+
         return False
-
-
-    paths = list(filter(script_exists,
-                        filter(os.path.exists,
-                               map(script_dir, sysconfig.get_scheme_names()))))
+
+    paths = list(
+        filter(
+            script_exists,
+            filter(os.path.exists, map(script_dir, sysconfig.get_scheme_names())),
+        )
+    )
 
     if paths:
         return Path(paths[0]) / SCRIPT_NAME
-    
+
     return None
 
+
 if __name__ == "__main__":
     maturin = get_maturin_path()
     if maturin is None:
-        print('Unable to find `maturin` script')
+        print("Unable to find `maturin` script")
         exit(1)
 
     os.execv(maturin, [str(maturin)] + sys.argv[1:])