Update license headers everywhere
License headers should be a range, not just the current year.
diff --git a/LICENSE.txt b/LICENSE.txt
index 858e024..413e30f 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -1,4 +1,4 @@
-Copyright (c) 2017 Uber Technologies, Inc.
+Copyright (c) 2017-2021 Uber Technologies, Inc.
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
diff --git a/error.go b/error.go
index 2f05442..faa0a05 100644
--- a/error.go
+++ b/error.go
@@ -1,4 +1,4 @@
-// Copyright (c) 2020 Uber Technologies, Inc.
+// Copyright (c) 2017-2021 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
diff --git a/error_test.go b/error_test.go
index e79669f..3dd4884 100644
--- a/error_test.go
+++ b/error_test.go
@@ -1,4 +1,4 @@
-// Copyright (c) 2019 Uber Technologies, Inc.
+// Copyright (c) 2017-2021 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
diff --git a/example_test.go b/example_test.go
index 6e59274..e46a633 100644
--- a/example_test.go
+++ b/example_test.go
@@ -1,4 +1,4 @@
-// Copyright (c) 2017 Uber Technologies, Inc.
+// Copyright (c) 2017-2021 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
