Update cocoapods (#1060)

CGRPCZlib.podspec

@@ -2,7 +2,7 @@ Pod::Spec.new do |s|
 
     s.name = 'CGRPCZlib'
     s.module_name = 'CGRPCZlib'
-    s.version = '1.0.0-alpha.20'
+    s.version = '1.0.0-alpha.21'
     s.license = { :type => 'Apache 2.0', :file => 'LICENSE' }
     s.summary = 'Compression library that provides in-memory compression and decompression functions'
     s.homepage = 'https://www.grpc.io'

gRPC-Swift-Plugins.podspec

@@ -1,7 +1,7 @@
 Pod::Spec.new do |s|
 
     s.name = 'gRPC-Swift-Plugins'
-    s.version = '1.0.0-alpha.20'
+    s.version = '1.0.0-alpha.21'
     s.license = { :type => 'Apache 2.0', :file => 'LICENSE' }
     s.summary = 'Swift gRPC code generator plugin binaries'
     s.homepage = 'https://www.grpc.io'

gRPC-Swift.podspec

@@ -2,7 +2,7 @@ Pod::Spec.new do |s|
 
     s.name = 'gRPC-Swift'
     s.module_name = 'GRPC'
-    s.version = '1.0.0-alpha.20'
+    s.version = '1.0.0-alpha.21'
     s.license = { :type => 'Apache 2.0', :file => 'LICENSE' }
     s.summary = 'Swift gRPC code generator plugin and runtime library'
     s.homepage = 'https://www.grpc.io'
@@ -18,11 +18,11 @@ Pod::Spec.new do |s|
     s.source_files = 'Sources/GRPC/**/*.{swift,c,h}'
 
     s.dependency 'Logging', '>= 1.4.0', '< 2'
-    s.dependency 'SwiftNIO', '>= 2.22.0', '< 3'
-    s.dependency 'SwiftNIOHTTP2', '>= 1.14.1', '< 2'
-    s.dependency 'SwiftNIOSSL', '>= 2.8.0', '< 3'
-    s.dependency 'SwiftNIOTransportServices', '>= 1.6.0', '< 2'
-    s.dependency 'SwiftProtobuf', '>= 1.9.0', '< 2'
+    s.dependency 'SwiftNIO', '>= 2.25.0', '< 3'
+    s.dependency 'SwiftNIOHTTP2', '>= 1.16.0', '< 2'
+    s.dependency 'SwiftNIOSSL', '>= 2.10.1', '< 3'
+    s.dependency 'SwiftNIOTransportServices', '>= 1.9.1', '< 2'
+    s.dependency 'SwiftProtobuf', '>= 1.13.0', '< 2'
     s.dependency 'CGRPCZlib', s.version.to_s
 
 end