Fix typo.

ca/mutable_tls_config.go

@@ -76,14 +76,14 @@ func (c *mutableTLSConfig) Reload() {
 	c.Unlock()
 }
 
-// AddImmutableClientCACert add an in-mutable cert to ClientCAs.
+// AddImmutableClientCACert add an immutable cert to ClientCAs.
 func (c *mutableTLSConfig) AddImmutableClientCACert(cert *x509.Certificate) {
 	c.Lock()
 	c.clientCerts = append(c.clientCerts, cert)
 	c.Unlock()
 }
 
-// AddImmutableRootCACert add an in-mutable cert to RootCas.
+// AddImmutableRootCACert add an immutable cert to RootCas.
 func (c *mutableTLSConfig) AddImmutableRootCACert(cert *x509.Certificate) {
 	c.Lock()
 	c.rootCerts = append(c.rootCerts, cert)