Fixed error cause by wrong visibility.

Error around line 217: RuntimeError: requested confidential method
"findLine" (defined at errormessages:240) from outside.
Called Module<parser>.parse (defined at parser:3468 in parser module)
at minigrace:55
Called NativePrelude.while()do (defined at unknown:0 in
StandardPrelude module) at parser:3521
Called Block[parser:3521].apply (defined at unknown:0) at
lexer:574
Called Block[parser:3521]._apply (defined at parser:3506) at
lexer:574
Called Module<parser>.statement (defined at parser:3304 in
parser module) at parser:3512
Called Module<parser>.checkUnexpectedTokenAfterStatement
(defined at parser:3397 in parser module) at parser:3366
Called suggestion.addLine (defined at errormessages:216 in
object at errormessages:440) at util:28
Called suggestion.findLine (defined at errormessages:240
in object at errormessages:440) at errormessages:217