lower version, for example 2.6.8
```properties
dubbo.provider.version=1.0
```

2.7.6 failed to recognize the provider url with 'default.version=1.0' key,  it only takes 'version.1.0' into consideration.

* @return
     */
    public String getColonSeparatedKey() {
        StringBuilder serviceNameBuilder = new StringBuilder();
        serviceNameBuilder.append(this.getServiceInterface());
        append(serviceNameBuilder, VERSION_KEY, false);
        append(serviceNameBuilder, GROUP_KEY, false);
        return serviceNameBuilder.toString();
    }
    private void append(StringBuilder target, String parameterName, boolean first) {
        String parameterValue = this.getParameter(parameterName);
        if (!StringUtils.isBlank(parameterValue)) {
            if (!first) {
                target.append(":");
            }
            target.append(parameterValue);
        } else {
            target.append(":");
        }
    }
    /**
     * The format of return value is '{group}/{interfaceName}:{version}'
     *
     * @return
     */
    public String getServiceKey() {
        if (serviceKey != null) {
            return serviceKey;
        }
        String inf = getServiceInterface();