fix: error about dynamic project version (#235)

* Fixed error in document regarding `Get with a specific function` section

* Fixed the error of not correctly parsing single literal parameters.

docs/metadata.md

@@ -87,13 +87,13 @@ def format_version(version: SCMVersion) -> str:
 ```toml
 [tool.pdm.version]
 source = "call"
-getter = "mypackage.version.get_version"
+getter = "mypackage.version:get_version"
 ```
 
 You can also supply it with literal arguments:
 
 ```toml
-getter = "mypackage.version.get_version('dev')"
+getter = "mypackage.version:get_version('dev')"
 ```
 
 ### Writing dynamic version to file

src/pdm/backend/utils.py

@@ -215,7 +215,10 @@ def evaluate_module_attribute(
         obj: Any = functools.reduce(getattr, attrs, module)
         args_group = matched.group(3)
         if args_group:
+            # make tuple
+            args_group = args_group.strip()[:-1] + ",)"
             args = ast.literal_eval(args_group)
+
         else:
             args = ()
         return obj, args