Fix version extraction code

Author: virtuald

robotpy_build/setup.py

@@ -104,15 +104,16 @@ def _generate_version(self):
 
             # Create the version.py file
             with open(version_file, "w") as fp:
-                fp.write("# Autogenerated by setup.py\n__version__ = '{0}'".format(v))
+                fp.write(f'# Autogenerated by setup.py\n__version__ = "{v}"\n')
 
+        version = "master"
         if exists(version_file):
+            env = {}
             with open(version_file, "r") as fp:
-                exec(fp.read(), locals())
-        else:
-            __version__ = "master"
+                exec(fp.read(), env)
+            version = env.get("__version__", version)
 
-        return __version__
+        return version
 
     def _collect_wrappers(self):