Fix the behavior of the ~= operator (#1481)

Fixes #1153

poetry/semver/__init__.py

@@ -79,7 +79,7 @@ def parse_single_constraint(constraint):  # type: (str) -> VersionConstraint
             low = version
             high = version.stable.next_major
         else:
-            low = Version(version.major, version.minor, 0)
+            low = Version(version.major, version.minor, version.patch)
             high = version.stable.next_minor
 
         return VersionRange(

tests/semver/test_main.py

@@ -67,7 +67,7 @@ def test_parse_constraint_wildcard(input, constraint):
         ("~0.3", VersionRange(Version(0, 3, 0), Version(0, 4, 0), True)),
         ("~3.5", VersionRange(Version(3, 5, 0), Version(3, 6, 0), True)),
         ("~=3.5", VersionRange(Version(3, 5, 0), Version(4, 0, 0), True)),  # PEP 440
-        ("~=3.5.3", VersionRange(Version(3, 5, 0), Version(3, 6, 0), True)),  # PEP 440
+        ("~=3.5.3", VersionRange(Version(3, 5, 3), Version(3, 6, 0), True)),  # PEP 440
     ],
 )
 def test_parse_constraint_tilde(input, constraint):