Simplify frule for Base.tail (#650)

* rm Tuple

* versions

Author: mcabbott

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.39.0"
+version = "1.39.1"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
@@ -14,7 +14,7 @@ SparseArrays = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
 [compat]
-ChainRulesCore = "1.12"
+ChainRulesCore = "1.15.3"
 ChainRulesTestUtils = "1.5"
 Compat = "3.42.0, 4"
 FiniteDifferences = "0.12.20"

src/rulesets/Base/indexing.jl

@@ -101,7 +101,7 @@ end
 
 function frule((_, ẋ), ::typeof(Base.tail), x::Tuple)
     y = Base.tail(x)
-    return y, Tangent{typeof(y)}(Base.tail(Tuple(ẋ))...)
+    return y, Tangent{typeof(y)}(Base.tail(ẋ)...)
 end
 
 function rrule(::typeof(Base.tail), x::T) where {T<:Tuple}