Fix toml module not updating content

poetry/toml/cascadedict.py

@@ -32,6 +32,10 @@ class CascadeDict:
         raise KeyError
 
     def __setitem__(self, key, value):
+        for d in self._internal_dicts[1:]:
+            if key in d:
+                d[key] = value
+
         self._internal_dicts[0][key] = value
 
     def get(self, item, default=None):

tests/toml/test_toml.py

+from poetry.toml import dumps
 from poetry.toml import loads
 
 from poetry.toml.prettify.errors import TOMLError
@@ -262,3 +263,27 @@ last_name = "Springsteen"
 def non_empty(iterable):
     return tuple(filter(bool, iterable))
 
+
+def test_set_elements():
+    t = """\
+[tool.poetry]
+name = "poetry"
+version = "0.1.0"
+
+[tool.poetry.dependencies]
+python = "^3.6"   
+"""
+    parsed = loads(t)
+
+    content = parsed['tool']['poetry']
+    assert content['name'] == 'poetry'
+    assert content['version'] == '0.1.0'
+
+    content['version'] = '0.2.0'
+    t = dumps(parsed)
+
+    parsed = loads(t)
+
+    content = parsed['tool']['poetry']
+    assert content['name'] == 'poetry'
+    assert content['version'] == '0.2.0'