replace deprecated uses of `exec`

def versionMinor = 13

def versionPatch = 11

def getGitHash = { ->

    def stdOut = new ByteArrayOutputStream()

    exec {

def getGitHashProvider = providers.exec {

    commandLine 'git', 'log', '--pretty=format:%h', '-n', '1'

        standardOutput = stdOut

}

    return stdOut.toString().trim()

def getGitHash = {

    return getGitHashProvider.standardOutput.asText.get().trim()

}

def getDate = { ->