update regex for version bump (#511)

# Conflicts:
#	.bumpversion.cfg

.bumpversion.cfg

@@ -1,11 +1,17 @@
 [bumpversion]
 current_version = 1.3.0
-parse = (?P<major>\d+)
-	\.(?P<minor>\d+)
-	\.(?P<patch>\d+)
-	((?P<prerelease>a|b|rc)
-	(?P<num>\d+)  # pre-release version num
-	)(\.(?P<nightly>[a-z..0-9]+)
+
+# `parse` allows parsing the version into the parts we need to check.  There are some
+# unnamed groups and that's okay because they do not need to be audited.  If any part
+# of the version passed and does not match the regex, it will fail.
+# expected matches: `1.5.0`, `1.5.0a1`, `1.5.0a1.dev123457+nightly`
+# excepted failures: `1`, `1.5`, `1.5.2-a1`, `text1.5.0`
+parse = (?P<major>[\d]+) # major version number
+	\.(?P<minor>[\d]+) # minor version number
+	\.(?P<patch>[\d]+) # patch version number
+	(((?P<prekind>a|b|rc) # optional pre-release type
+	?(?P<num>[\d]+?)) # optional pre-release version number
+	\.?(?P<nightly>[a-z0-9]+\+[a-z]+)? # optional nightly release indicator
 	)?
 serialize =
 	{major}.{minor}.{patch}{prerelease}{num}.{nightly}