Make date regexp more flexible so that we don't have to update it yearly

hack/boilerplate/boilerplate.py

@@ -149,8 +149,8 @@ def get_regexs():
     regexs = {}
     # Search for "YEAR" which exists in the boilerplate, but shouldn't in the real thing
     regexs["year"] = re.compile( 'YEAR' )
-    # dates can be 2014, 2015, 2016, 2017, or 2018, company holder names can be anything
-    regexs["date"] = re.compile( '(2014|2015|2016|2017|2018)' )
+    # dates can be 2010 to 2039
+    regexs["date"] = re.compile( '(20[123]\d)' )
     # strip // +build \n\n build constraints
     regexs["go_build_constraints"] = re.compile(r"^(// \+build.*\n)+\n", re.MULTILINE)
     # strip #!.* from shell scripts