message: subscriber: use `f64` consts as module imports
  This fixes the build on Rust 1.42.0, where primitive types don't have
  associated consts. My bad!
diff: @@ -219,7 +219,7 @@ impl fmt::Display for ValueMatch {
  match self {
  ValueMatch::Bool(ref inner) => fmt::Display::fmt(inner, f),
  ValueMatch::F64(ref inner) => fmt::Display::fmt(inner, f),
  - ValueMatch::NaN => fmt::Display::fmt(&f64::NAN, f),
  + ValueMatch::NaN => fmt::Display::fmt(&std::f64::NAN, f),
  ValueMatch::I64(ref inner) => fmt::Display::fmt(inner, f),
  ValueMatch::U64(ref inner) => fmt::Display::fmt(inner, f),
  ValueMatch::Pat(ref inner) => fmt::Display::fmt(inner, f),
  @@ -355,7 +355,9 @@ impl<'a> Visit for MatchVisitor<'a> {
  Some((ValueMatch::NaN, ref matched)) if value.is_nan() => {
  matched.store(true, Release);
  }
  - Some((ValueMatch::F64(ref e), ref matched)) if (value - *e).abs() < f64::EPSILON => {
  + Some((ValueMatch::F64(ref e), ref matched))
  + if (value - *e).abs() < std::f64::EPSILON =>
  + {
  matched.store(true, Release);
  }
  _ => {}
  