[turbofan] Math.random never produces -0.

R=mvstanton@chromium.org
BUG=v8:5267,v8:5270

Review-Url: https://codereview.chromium.org/2312693002
Cr-Commit-Position: refs/heads/master@{#39162}

src/compiler/typer.cc

@@ -1295,7 +1295,7 @@ Type* Typer::Visitor::JSCallFunctionTyper(Type* fun, Typer* t) {
     if (function->shared()->HasBuiltinFunctionId()) {
       switch (function->shared()->builtin_function_id()) {
         case kMathRandom:
-          return Type::OrderedNumber();
+          return Type::PlainNumber();
         case kMathFloor:
         case kMathCeil:
         case kMathRound: