Correct a copy of misspellings found by misspell.

spew/dump_test.go

@@ -70,7 +70,7 @@ import (
 	"github.com/davecgh/go-spew/spew"
 )
 
-// dumpTest is used to describe a test to be perfomed against the Dump method.
+// dumpTest is used to describe a test to be performed against the Dump method.
 type dumpTest struct {
 	in    interface{}
 	wants []string

spew/format_test.go

@@ -75,7 +75,7 @@ import (
 	"github.com/davecgh/go-spew/spew"
 )
 
-// formatterTest is used to describe a test to be perfomed against NewFormatter.
+// formatterTest is used to describe a test to be performed against NewFormatter.
 type formatterTest struct {
 	format string
 	in     interface{}