Add is_prerelease method in SemverVersion

Signed-off-by: Keshav Priyadarshi <git@keshav.space>

Author: keshav-space

src/univers/versions.py

@@ -226,6 +226,9 @@ def next_minor(self):
     def next_patch(self):
         return self.value and SemverVersion(str(self.value.next_patch()))
 
+    def is_prerelease(self):
+        return bool(self.prerelease)
+
 
 def is_even(s):
     """