Piggy back tweak in parser

(unrelated to PR, but it's too much hassle to open a separate one to
get this in)

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1144,13 +1144,12 @@ object Parsers {
         val name = bindingName()
         val t =
           if (in.token == COLON && location == Location.InBlock) {
-            if (false) // Don't error yet, as the alternative syntax "implicit (x: T) => ... "
-                       // is not supported by Scala2.x
+            if (ctx.settings.strict.value)
+                // Don't error in non-strict mode, as the alternative syntax "implicit (x: T) => ... "
+                // is not supported by Scala2.x
               migrationWarningOrError(s"This syntax is no longer supported; parameter needs to be enclosed in (...)")
-
             in.nextToken()
             val t = infixType()
-
             if (false && in.isScala2Mode) {
               patch(source, Position(start), "(")
               patch(source, Position(in.lastOffset), ")")