Fixes #1238 Swift target

[janyou]

@parrt Suggestion: To make a similar page to collate common issues information may be better.
@antlr/antlr-targets can read and modify it.

Common issues handling information

Issue ID	Antlr Target	Status	Accepted by
->	Java	Done	xxx
-	C#	In progress	xxx
-	Javascript	Done	xxx
#1238	Python2	Todo
-	Python3	Todo
-	Go	Todo
-	C++	Todo
<-	Swift	Todo
->	Java	Done	xxx
-	C#	In progress	xxx
-	Javascript	Done	xxx
#994	Python2	Todo
-	Python3	Todo
-	Go	Todo
-	C++	Todo
<-	Swift	Todo

[mike-lischke]

@janyou I have no idea what this table means. Can you explain please?

Why don't just make your PR reference the original Java implementation and focus only on your target? Others have to create PRs as well, they cannot use yours.

[janyou]

Common issues handling information

Issue ID	Antlr Target	Status	Accepted by
#1238	Java	Done	xxx
#1238	C#	In progress	xxx
#1238	Javascript	Done	xxx
#1238	Python2	Todo
#1238	Python3	Todo
#1238	Go	Todo
#1238	C++	Todo
#1238	Swift	Todo
#994	Java	Done	xxx
#994	C#	In progress	xxx
#994	Javascript	Done	xxx
#994	Python2	Todo
#994	Python3	Todo
#994	Go	Todo
#994	C++	Todo
#994	Swift	Todo

Purposes:

1. Avoid duplication of effort
   When a target has more than one maintainer, one of them can accept the fix task and modify the status.

2. Avoid missing
   The maintainers of each target can get information on common issues from this page.
   Parrt can check it before releasing.

[janyou]

the PR is not correct