goautomock tests fail

[Monnoroch]

I'm trying to run tests for this project and can't generate mocks (which is a required step before actually running tests):

$ go version
go version go1.8 linux/amd64

/go/src/github.com/ernesto-jimenez/gogen$ go generate github.com/ernesto-jimenez/gogen/...
Generating mock for Writer in io_writer_mock_test.go
Generating mock for ByteScanner in io_byte_scanner_mock_test.go
Generating mock for CookieJar in http_cookie_jar_mock_test.go
interface unexported missing
exit status 1
automock/generator_test.go:121: running "go": exit status 1
Generating func (*SimpleStruct) UnmarshalMap(map[string]interface{}) error
Generating func (*Array) UnmarshalMap(map[string]interface{}) error
Generating func (*Composed) UnmarshalMap(map[string]interface{}) error
Generating func (*Nested) UnmarshalMap(map[string]interface{}) error

I'm using the last version of the project.