Fix -strict-concurrency help text to say minimal instead of explicit

Author: gwynne

include/swift/Option/Options.td

@@ -794,7 +794,7 @@ def warn_concurrency : Flag<["-"], "warn-concurrency">,
 def strict_concurrency : Joined<["-"], "strict-concurrency=">,
   Flags<[FrontendOption, DoesNotAffectIncrementalBuild]>,
   HelpText<"Specify the how strict concurrency checking will be. The value may "
-           "be 'explicit' (most 'Sendable' checking is disabled), "
+           "be 'minimal' (most 'Sendable' checking is disabled), "
            "'targeted' ('Sendable' checking is enabled in code that uses the "
            "concurrency model, or 'complete' ('Sendable' and other checking is "
            "enabled for all code in the module)">;