GELF output: GELF message has invalid timestamp

[8ear]

Hi,
I added the graygelf npm package and builded from your sematext/logagent:latest my customized logagent container.

Now I will transfer my collected logs from logagent to Graylog. But with the gelf-output I will only get the following errors at the Graylog side:

2020-05-02 09:26:04,078 WARN : org.graylog2.inputs.codecs.GelfCodec - GELF message <f19b14d3-8c56-11ea-971d-02420a2f0208> (received from <xx.xx.xx.xx:44149>) has invalid "timestamp": 2020-05-02T09:26:03.666Z  (type: STRING)
2020-05-02 09:26:04,078 WARN : org.graylog2.inputs.codecs.GelfCodec - GELF message <f19b14d8-8c56-11ea-971d-02420a2f0208> (received from <xx.xx.xx.xx:44149>) has invalid "timestamp": 2020-05-02T09:26:03.667Z  (type: STRING)
2020-05-02 09:26:04,078 WARN : org.graylog2.inputs.codecs.GelfCodec - GELF message <f19b14d9-8c56-11ea-971d-02420a2f0208> (received from <xx.xx.xx.xx:44149>) has invalid "timestamp": 2020-05-02T09:26:03.668Z  (type: STRING)
2020-05-02 09:26:04,078 WARN : org.graylog2.inputs.codecs.GelfCodec - GELF message <f19b14da-8c56-11ea-971d-02420a2f0208> (received from <xx.xx.xx.xx:44149>) has invalid "timestamp": 2020-05-02T09:26:03.668Z  (type: STRING)

How I can change the timestamp?

Config:

# /etc/sematext/logagent.conf

# Global options
options:
    # print stats every 60 seconds 
    printStats: 60
    # don't write parsed logs to stdout
    suppress: true
    # Enable/disable GeoIP lookups
    # Startup of logagent might be slower, when downloading the GeoIP database
    geoipEnabled: true
    # Directory to store Logagent status and temporary files
    # this is equals to LOGS_TMP_DIR env variable 
    diskBufferDir: /tmp/sematext-logagent
    includeOriginalLine: false

input:
    # a list of glob patterns to watch files to tail
    files:
        - "/host/var/log/**/*.log"
        - "/var/log/**/*.log"
    docker:
        module: docker-logs
        socket: /var/run/docker.sock
        labelFilter: com.docker.*,io.kubernetes.*,annotation.*
    syslog: # syslog udp
        address: 0.0.0.0
        port: 1514


outputFilter: 
    dockerEnrichment:
        module: docker-enrichment 
        autodetectSeverity: true
    geoip: 
        module: geoip
        fields: 
        - client_ip
        - remote_address

output:
    gelf:
        module: output-gelf
        host: graylog
        # graylog port (default: 12201)
        port: 12201
        # compression 'gzip' or 'deflate' (default: 'deflate')
        compressType: deflate
        # size of chunked messages in bytes (default: 1240)
        chunkSize: 1240

    stdout: pretty

Is there a other possible way to get the logs from logagent to Graylog?

Kind regards