https://github.com/FluxML/Tracker.jl/commit/f6550ba38a9ea5802e2de4fa9c939929ba711f0d.patch
from an upstream pull request
https://github.com/FluxML/Tracker.jl/pull/94


From f6550ba38a9ea5802e2de4fa9c939929ba711f0d Mon Sep 17 00:00:00 2001
From: Michael Abbott <me@escbook>
Date: Wed, 3 Feb 2021 22:58:33 +0100
Subject: [PATCH] two fixes for 1.6

---
 src/lib/array.jl | 2 +-
 src/lib/real.jl  | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/lib/array.jl b/src/lib/array.jl
index 92f2b39..f8cbbac 100644
--- a/src/lib/array.jl
+++ b/src/lib/array.jl
@@ -298,7 +298,7 @@ Base.reverse(xs::TrackedArray; dims) = track(reverse, xs, dims = dims)
 @grad reverse(xs; dims) = reverse(data(xs), dims = dims), Δ -> (reverse(Δ, dims = dims), nothing)
 Base.reverse(xs::TrackedVector) = track(reverse, xs)
 @grad reverse(xs::TrackedVector) = reverse(data(xs)), Δ -> (reverse(Δ),)
-Base.reverse(xs::TrackedVector, start, stop) = track(reverse, xs, start, stop)
+Base.reverse(xs::TrackedVector, start::Integer, stop::Integer) = track(reverse, xs, start, stop)
 @grad reverse(xs, start, stop) = reverse(data(xs), start, stop), Δ -> (reverse(Δ, start, stop), nothing, nothing)
 
 function _kron(mat1::AbstractMatrix,mat2::AbstractMatrix)
diff --git a/src/lib/real.jl b/src/lib/real.jl
index 737afd8..e1975ac 100644
--- a/src/lib/real.jl
+++ b/src/lib/real.jl
@@ -55,6 +55,7 @@ for f in :[isinf, isnan, isfinite].args
 end
 
 Printf.fix_dec(x::TrackedReal, n::Int, a...) = Printf.fix_dec(data(x), n, a...)
+Printf.tofloat(x::TrackedReal) = Printf.tofloat(data(x))
 
 Base.float(x::TrackedReal) = x