This is mostly a bug fix release on runtime packages. It is safe to use 3.4.0 protoc packages for this release.

• Fixed the missing files in 3.4.0 tarballs, affecting windows and cmake users.
• C#: Fixed dotnet target platform to be net45 again.
• Ruby: Fixed a segmentation error when using maps in multi-threaded cases.
• PHP: php_generic_service file level option tag number (in descriptor.proto) has been reassigned to avoid conflicts.