pkg: spelling tweaks, A-H

R=ality, bradfitz, rsc, dsymonds, adg, qyzhai, dchest
CC=golang-dev
https://golang.org/cl/4536063
diff --git a/src/pkg/http/persist.go b/src/pkg/http/persist.go
index 4eb4ab0..62f9ff1 100644
--- a/src/pkg/http/persist.go
+++ b/src/pkg/http/persist.go
@@ -111,7 +111,7 @@
 	// Make sure body is fully consumed, even if user does not call body.Close
 	if lastbody != nil {
 		// body.Close is assumed to be idempotent and multiple calls to
-		// it should return the error that its first invokation
+		// it should return the error that its first invocation
 		// returned.
 		err = lastbody.Close()
 		if err != nil {