upgrade github.com/nishanths/exhaustive (#1246)

This pulls in a fix for handling of blank identifiers by the exhaustive
package.

Patch obtained by running:

```
go get github.com/nishanths/exhaustive
```

go.mod

@@ -34,7 +34,7 @@ require (
 	github.com/mitchellh/go-homedir v1.1.0
 	github.com/mitchellh/go-ps v1.0.0
 	github.com/nakabonne/nestif v0.3.0
-	github.com/nishanths/exhaustive v0.0.0-20200525081945-8e46705b6132
+	github.com/nishanths/exhaustive v0.0.0-20200708172631-8866003e3856
 	github.com/pkg/errors v0.9.1
 	github.com/ryancurrah/gomodguard v1.1.0
 	github.com/ryanrolds/sqlclosecheck v0.3.0

go.sum

@@ -259,8 +259,8 @@ github.com/nbutton23/zxcvbn-go v0.0.0-20180912185939-ae427f1e4c1d h1:AREM5mwr4u1
 github.com/nbutton23/zxcvbn-go v0.0.0-20180912185939-ae427f1e4c1d/go.mod h1:o96djdrsSGy3AWPyBgZMAGfxZNfgntdJG+11KU4QvbU=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e h1:fD57ERR4JtEqsWbfPhv4DMiApHyliiK5xCTNVSPiaAs=
 github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
-github.com/nishanths/exhaustive v0.0.0-20200525081945-8e46705b6132 h1:NjznefjSrral0MiR4KlB41io/d3OklvhcgQUdfZTqJE=
-github.com/nishanths/exhaustive v0.0.0-20200525081945-8e46705b6132/go.mod h1:wBEpHwM2OdmeNpdCvRPUlkEbBuaFmcK4Wv8Q7FuGW3c=
+github.com/nishanths/exhaustive v0.0.0-20200708172631-8866003e3856 h1:W3KBC2LFyfgd+wNudlfgCCsTo4q97MeNWrfz8/wSdSc=
+github.com/nishanths/exhaustive v0.0.0-20200708172631-8866003e3856/go.mod h1:wBEpHwM2OdmeNpdCvRPUlkEbBuaFmcK4Wv8Q7FuGW3c=
 github.com/oklog/ulid v1.3.1/go.mod h1:CirwcVhetQ6Lv90oh/F+FBtV6XMibvdAFo93nm5qn4U=
 github.com/onsi/ginkgo v1.6.0/go.mod h1:lLunBs/Ym6LB5Z9jYTR76FiuTmxDTDusOGeTQH+WWjE=
 github.com/onsi/ginkgo v1.12.0 h1:Iw5WCbBcaAAd0fpRb1c9r5YCylv4XDoCSigm1zLevwU=
@@ -373,8 +373,6 @@ github.com/uudashr/gocognit v1.0.1/go.mod h1:j44Ayx2KW4+oB6SWMv8KsmHzZrOInQav7D3
 github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=
 github.com/valyala/bytebufferpool v1.0.0/go.mod h1:6bBcMArwyJ5K/AmCkWv1jt77kVWyCJ6HpOuEn7z0Csc=
 github.com/valyala/fasthttp v1.12.0/go.mod h1:229t1eWu9UXTPmoUkbpN/fctKPBY4IJoFXQnxHGXy6E=
-github.com/valyala/quicktemplate v1.5.0 h1:2CUbkvZbxZ9m51wp5a2vzrbnv38Iocp0bMJomSmHyg0=
-github.com/valyala/quicktemplate v1.5.0/go.mod h1:v7yYWpBEiutDyNfVaph6oC/yKwejzVyTX/2cwwHxyok=
 github.com/valyala/quicktemplate v1.5.1 h1:JtrOtlRMP+pySF9dkPBfVfhZ3YHTitAJpMLNqT9ZjFk=
 github.com/valyala/quicktemplate v1.5.1/go.mod h1:v7yYWpBEiutDyNfVaph6oC/yKwejzVyTX/2cwwHxyok=
 github.com/valyala/tcplisten v0.0.0-20161114210144-ceec8f93295a/go.mod h1:v3UYOV9WzVtRmSR+PDvWpU/qWl4Wa5LApYYX4ZtKbio=