deps: bump github.com/Workiva/go-datastructures (#4519)

Bumps [github.com/Workiva/go-datastructures](https://github.com/Workiva/go-datastructures) from 1.0.50 to 1.0.51.
- [Release notes](https://github.com/Workiva/go-datastructures/releases)
- [Commits](https://github.com/Workiva/go-datastructures/compare/v1.0.50...v1.0.51)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

go.mod

@@ -4,7 +4,7 @@ go 1.13
 
 require (
 	github.com/ChainSafe/go-schnorrkel v0.0.0-20200102211924-4bcbc698314f
-	github.com/Workiva/go-datastructures v1.0.50
+	github.com/Workiva/go-datastructures v1.0.51
 	github.com/btcsuite/btcd v0.0.0-20190115013929-ed77733ec07d
 	github.com/btcsuite/btcutil v0.0.0-20180706230648-ab6388e0c60a
 	github.com/fortytw2/leaktest v1.3.0

go.sum

@@ -12,6 +12,8 @@ github.com/VividCortex/gohistogram v1.0.0 h1:6+hBz+qvs0JOrrNhhmR7lFxo5sINxBCGXrd
 github.com/VividCortex/gohistogram v1.0.0/go.mod h1:Pf5mBqqDxYaXu3hDrrU+w6nw50o/4+TcAqDqk/vUH7g=
 github.com/Workiva/go-datastructures v1.0.50 h1:slDmfW6KCHcC7U+LP3DDBbm4fqTwZGn1beOFPfGaLvo=
 github.com/Workiva/go-datastructures v1.0.50/go.mod h1:Z+F2Rca0qCsVYDS8z7bAGm8f3UkzuWYS/oBZz5a7VVA=
+github.com/Workiva/go-datastructures v1.0.51 h1:LJHjjfcv+1gH+1D1SgrjcrF8iSZkgsAdCjclvHvVecQ=
+github.com/Workiva/go-datastructures v1.0.51/go.mod h1:Z+F2Rca0qCsVYDS8z7bAGm8f3UkzuWYS/oBZz5a7VVA=
 github.com/aead/siphash v1.0.1/go.mod h1:Nywa3cDsYNNK3gaciGTWPwHt0wlpNV15vwmswBAUSII=
 github.com/afex/hystrix-go v0.0.0-20180502004556-fa1af6a1f4f5/go.mod h1:SkGFH1ia65gfNATL8TAiHDNxPzPdmEL5uirI2Uyuz6c=
 github.com/alecthomas/template v0.0.0-20160405071501-a0175ee3bccc/go.mod h1:LOuyumcjzFXgccqObfd/Ljyb9UuFJ6TxHnclSeseNhc=