Merge pull request #180 from MrMage/fix-podspec

 Fix the Podspec by only including `Sources/SwiftGRPC/*.swift`

SwiftGRPC.podspec

@@ -42,7 +42,7 @@ Pod::Spec.new do |s|
   #s.tvos.deployment_target = '9.0'
   #s.watchos.deployment_target = '2.0'
 
-  s.source_files = 'Sources/**/*.swift', 'Sources/CgRPC/shim/*.[ch]'
+  s.source_files = 'Sources/SwiftGRPC/*.swift', 'Sources/SwiftGRPC/**/*.swift', 'Sources/CgRPC/shim/*.[ch]'
   s.public_header_files = 'Sources/CgRPC/shim/cgrpc.h'
 
   s.dependency 'gRPC-Core', '~> 1.9.1'