Core: rectify function signature return type

This commit addresses a mistake in the `runAstNodeRules`
function where the return type was incorrectly specified.
The return type has now been corrected.

src/FSharpLint.Core/Application/Lint.fsi

@@ -129,7 +129,7 @@ module Lint =
           SyntaxArray: AbstractSyntaxArray.Node array }
 
     /// Runs all rules which take a node of the AST as input.
-    val runAstNodeRules : RunAstNodeRulesConfig -> Suggestion.LintWarning array * Context
+    val runAstNodeRules : RunAstNodeRulesConfig -> Suggestion.LintWarning [] * Context
 
     type RunLineRulesConfig = { LineRules: Configuration.LineRules 
                                 GlobalConfig: Rules.GlobalRuleConfig