Spell out 'certificates' rather than 'certs'

src/objective-c/GRPCClient/private/GRPCChannelPool.m

@@ -52,10 +52,10 @@ extern const char *kCFStreamVarName;
 #ifdef GRPC_COMPILE_WITH_CRONET
       if (![GRPCCall isUsingCronet]) {
 #endif
-        factory = [GRPCSecureChannelFactory factoryWithPEMRootCerts:_callOptions.PEMRootCertificates
-                                                         privateKey:_callOptions.PEMPrivateKey
-                                                          certChain:_callOptions.PEMCertChain
-                                                              error:&error];
+        factory = [GRPCSecureChannelFactory factoryWithPEMRootCertificates:_callOptions.PEMRootCertificates
+                                                                privateKey:_callOptions.PEMPrivateKey
+                                                                 certChain:_callOptions.PEMCertChain
+                                                                     error:&error];
         if (factory == nil) {
           NSLog(@"Error creating secure channel factory: %@", error);
         }

src/objective-c/GRPCClient/private/GRPCSecureChannelFactory.h

@@ -23,10 +23,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 @interface GRPCSecureChannelFactory : NSObject<GRPCChannelFactory>
 
-+ (nullable instancetype)factoryWithPEMRootCerts:(nullable NSString *)rootCerts
-                                      privateKey:(nullable NSString *)privateKey
-                                       certChain:(nullable NSString *)certChain
-                                           error:(NSError **)errorPtr;
++ (nullable instancetype)factoryWithPEMRootCertificates:(nullable NSString *)rootCerts
+                                             privateKey:(nullable NSString *)privateKey
+                                              certChain:(nullable NSString *)certChain
+                                                  error:(NSError **)errorPtr;
 
 - (nullable grpc_channel *)createChannelWithHost:(NSString *)host
                                      channelArgs:(nullable NSDictionary *)args;

src/objective-c/GRPCClient/private/GRPCSecureChannelFactory.m

@@ -29,10 +29,10 @@ NS_ASSUME_NONNULL_BEGIN
   grpc_channel_credentials *_channelCreds;
 }
 
-+ (nullable instancetype)factoryWithPEMRootCerts:(nullable NSString *)rootCerts
-                                      privateKey:(nullable NSString *)privateKey
-                                       certChain:(nullable NSString *)certChain
-                                           error:(NSError **)errorPtr {
++ (nullable instancetype)factoryWithPEMRootCertificates:(nullable NSString *)rootCerts
+                                             privateKey:(nullable NSString *)privateKey
+                                              certChain:(nullable NSString *)certChain
+                                                  error:(NSError **)errorPtr {
   return [[self alloc] initWithPEMRootCerts:rootCerts
                                  privateKey:privateKey
                                   certChain:certChain