docs: update license year

Yukaii · Yukaii · commit e0b93a136867 · 2022-03-09T13:26:35.000+08:00
diff --git a/LICENSE b/LICENSE
@@ -1,4 +1,4 @@
-Copyright 2020 HackMD
+Copyright 2022 HackMD
 
 Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
 

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-Copyright 2020 HackMD`
	`1`	`+Copyright 2022 HackMD`
`2`	`2`
`3`	`3`	`Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:`
`4`	`4`