all: apply gofumpt (#79)

Apply @mvdan's opinionated gofumpt formatter across the codebase.

operand/checks.go

@@ -1,8 +1,6 @@
 package operand
 
-import (
-	"github.com/mmcloughlin/avo/reg"
-)
+import "github.com/mmcloughlin/avo/reg"
 
 // Pure type assertion checks:
 

operand/make_const.go

@@ -15,9 +15,7 @@ import (
 	"strconv"
 )
 
-var (
-	output = flag.String("output", "", "path to output file (default stdout)")
-)
+var output = flag.String("output", "", "path to output file (default stdout)")
 
 func PrintConstType(w io.Writer, name, typ, format string, size int, doc string) {
 	r := typ[0]