Use 'Any' if specific version is required

Earlier the output said 'None' if a dependency didn't mention a specific
version to install. 'Any' is definitely a better term for this case.

Fixes #57

pipdeptree.py

@@ -260,10 +260,10 @@ class ReqPackage(Package):
 
     def render_as_branch(self, frozen):
         if not frozen:
+            req_ver = self.version_spec if self.version_spec else 'Any'
             return (
                 '{0} [required: {1}, installed: {2}]'
-                ).format(self.project_name, self.version_spec,
-                         self.installed_version)
+                ).format(self.project_name, req_ver, self.installed_version)
         else:
             return self.render_as_root(frozen)
 

tests/test_pipdeptree.py

@@ -87,7 +87,7 @@ def test_ReqPackage_render_as_branch():
     assert mks1.project_name == 'markupsafe'
     assert mks1.installed_version == '0.18'
     assert mks1.version_spec is None
-    assert mks1.render_as_branch(False) == 'markupsafe [required: None, installed: 0.18]'
+    assert mks1.render_as_branch(False) == 'markupsafe [required: Any, installed: 0.18]'
     assert mks1.render_as_branch(True) == 'MarkupSafe==0.18'
     mks2 = find_req('markupsafe', 'mako')
     assert mks2.project_name == 'MarkupSafe'
@@ -147,9 +147,9 @@ def test_render_tree_cyclic_dependency():
     tree_str = render_tree(tree, list_all=True)
     lines = set(tree_str.split('\n'))
     assert 'CircularDependencyA==0.0.0' in lines
-    assert '  - CircularDependencyB [required: None, installed: 0.0.0]' in lines
+    assert '  - CircularDependencyB [required: Any, installed: 0.0.0]' in lines
     assert 'CircularDependencyB==0.0.0' in lines
-    assert '  - CircularDependencyA [required: None, installed: 0.0.0]' in lines
+    assert '  - CircularDependencyA [required: Any, installed: 0.0.0]' in lines
 
 
 def test_render_tree_freeze_cyclic_dependency():