go.mod: golang_protobuf_extensions v1.0.4 - prevent incompatible versions

This module made a whoopsie, and updated to `google.golang.org/protobuf`
in a patch release, but `google.golang.org/protobuf` is not backward
compatible with `github.com/golang/protobuf`.

Updating the minimum version to v1.0.4 which corrects this, to prevent
users of containerd as a module from accidentally pulling in the wrong
version:

- v1.0.3 switched to use `google.golang.org/protobuf`; https://github.com/matttproud/golang_protobuf_extensions/compare/v1.0.2..v1.0.3
- This was reverted in v1.0.4 (which is the same as v1.0.2); https://github.com/matttproud/golang_protobuf_extensions/compare/v1.0.3..v1.0.4
- And a `v2` was created instead; https://github.com/matttproud/golang_protobuf_extensions/releases/tag/v2.0.0

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

integration/client/go.sum

@@ -810,7 +810,7 @@ github.com/mattn/go-isatty v0.0.3/go.mod h1:M+lRXTBqGeGNdLjl/ufCoiOlB5xdOkqRJdNx
 github.com/mattn/go-shellwords v1.0.6/go.mod h1:3xCvwCdWdlDJUrvuMn7Wuy9eWs4pE8vqg+NOMyg4B2o=
 github.com/mattn/go-shellwords v1.0.12/go.mod h1:EZzvwXDESEeg03EKmM+RmDnNOPKG4lLtQsUlTZDWQ8Y=
 github.com/matttproud/golang_protobuf_extensions v1.0.1/go.mod h1:D8He9yQNgCq6Z5Ld7szi9bcBfOoFv/3dc6xSMkL2PC0=
-github.com/matttproud/golang_protobuf_extensions v1.0.2/go.mod h1:BSXmuO+STAnVfrANrmjBb36TMTDstsz7MSK+HVaYKv4=
+github.com/matttproud/golang_protobuf_extensions v1.0.4/go.mod h1:BSXmuO+STAnVfrANrmjBb36TMTDstsz7MSK+HVaYKv4=
 github.com/maxbrunsfeld/counterfeiter/v6 v6.2.2/go.mod h1:eD9eIE7cdwcMi9rYluz88Jz2VyhSmden33/aXg4oVIY=
 github.com/miekg/dns v1.0.14/go.mod h1:W1PPwlIAgtquWBMBEV9nkV9Cazfe8ScdGz/Lj7v3Nrg=
 github.com/miekg/pkcs11 v1.1.1/go.mod h1:XsNlhZGX73bx86s2hdc/FuaLm2CPZJemRLMA+WTFxgs=