Fix references to old backoff "config" terminology.

Author: jmalloc

Diff for: backoff/counter.go

@@ -12,7 +12,7 @@ import (
 // introduce delays between retries.
 type Counter struct {
 	// Strategy is used to calculate the delay duration.
-	// If it is nil, DefaultBackoffConfig is used.
+	// If it is nil, DefaultStrategy is used.
 	Strategy Strategy
 
 	// failures is the number of successive failures that have occurred.

Diff for: backoff/counter_test.go

@@ -37,7 +37,7 @@ var _ = Describe("type Counter", func() {
 		It("uses the default strategy if none is specified", func() {
 			counter.Strategy = nil
 
-			// The default configuration uses FullJitter, so this is hard to
+			// The default strategy uses FullJitter, so this is hard to
 			// test well, but essentially we're ensuring it doesn't panic.
 
 			Expect(counter.Fail(nil)).To(BeNumerically("<=", 3*time.Second))