Squashed commit of the following:

commit 95479c8ad744db48386a5c78e54ef8da80e9120b
Author: Chris Lane <chris@chris-allen-lane.com>
Date:   Wed Apr 28 12:26:32 2021 -0400

    chore(version): bump version to 4.2.1

commit 6956f51cae
Author: Chris Lane <chris@chris-allen-lane.com>
Date:   Wed Apr 28 12:24:21 2021 -0400

    fix(Makefile): `vendor-update`

    Update the `vendor-update` build target to run `go mod vendor` after
    updating dependencies.

commit 0aca411279
Author: Chris Lane <chris@chris-allen-lane.com>
Date:   Wed Apr 28 12:23:24 2021 -0400

    chore(deps): update dependencies

commit e847956b02
Author: Chris Lane <chris@chris-allen-lane.com>
Date:   Wed Apr 28 08:26:51 2021 -0400

    chore(deps): build updates

    - Upgrade `go` to `1.16.3`

    - Attempt to fix build errors regarding dependencies

vendor/github.com/alecthomas/chroma/styles/xcode-dark.go

@@ -0,0 +1,62 @@
+package styles
+
+import (
+	"github.com/alecthomas/chroma"
+)
+
+var (
+	// Inspired by Apple's Xcode "Default (Dark)" Theme
+	background                  = "#1F1F24"
+	plainText                   = "#FFFFFF"
+	comments                    = "#6C7986"
+	strings                     = "#FC6A5D"
+	numbers                     = "#D0BF69"
+	keywords                    = "#FC5FA3"
+	preprocessorStatements      = "#FD8F3F"
+	typeDeclarations            = "#5DD8FF"
+	otherDeclarations           = "#41A1C0"
+	otherFunctionAndMethodNames = "#A167E6"
+	otherTypeNames              = "#D0A8FF"
+)
+
+// Xcode dark style
+var XcodeDark = Register(chroma.MustNewStyle("xcode-dark", chroma.StyleEntries{
+	chroma.Background: plainText + " bg: " + background,
+
+	chroma.Comment:          comments,
+	chroma.CommentMultiline: comments,
+	chroma.CommentPreproc:   preprocessorStatements,
+	chroma.CommentSingle:    comments,
+	chroma.CommentSpecial:   comments + " italic",
+
+	chroma.Error: "#960050",
+
+	chroma.Keyword:            keywords,
+	chroma.KeywordConstant:    keywords,
+	chroma.KeywordDeclaration: keywords,
+	chroma.KeywordReserved:    keywords,
+
+	chroma.LiteralNumber:        numbers,
+	chroma.LiteralNumberBin:     numbers,
+	chroma.LiteralNumberFloat:   numbers,
+	chroma.LiteralNumberHex:     numbers,
+	chroma.LiteralNumberInteger: numbers,
+	chroma.LiteralNumberOct:     numbers,
+
+	chroma.LiteralString:         strings,
+	chroma.LiteralStringEscape:   strings,
+	chroma.LiteralStringInterpol: plainText,
+
+	chroma.Name:              plainText,
+	chroma.NameBuiltin:       otherTypeNames,
+	chroma.NameBuiltinPseudo: otherFunctionAndMethodNames,
+	chroma.NameClass:         typeDeclarations,
+	chroma.NameFunction:      otherDeclarations,
+	chroma.NameVariable:      otherDeclarations,
+
+	chroma.Operator: plainText,
+
+	chroma.Punctuation: plainText,
+
+	chroma.Text: plainText,
+}))