Fix spelling of presign

Issue #547

Author: MatthewJohn

terrareg/server/api/module_version_source_download.py

@@ -28,7 +28,7 @@ def _get(self, namespace, name, provider, version, presign=None):
             # Remove last section of path (i.e. the file name)
             del path_parts[-1]
 
-            # If path ends with the presign key, remove it
+            # If path ends with the pre-sign key, remove it
             if presign and path_parts[-1] == presign:
                 del path_parts[-1]
             path = '/'.join(path_parts)