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.

if (inf == null) {
            return null;
        }
        serviceKey = buildKey(inf, getParameter(GROUP_KEY), getParameter(VERSION_KEY));
        return serviceKey;
    }
    /**
     * The format of return value is '{group}/{path/interfaceName}:{version}'
     *
     * @return
     */
    public String getPathKey() {
        String inf = StringUtils.isNotEmpty(path) ? path : getServiceInterface();
        if (inf == null) {
            return null;
        }
        return buildKey(inf, getParameter(GROUP_KEY), getParameter(VERSION_KEY));
    }
    public static String buildKey(String path, String group, String version) {
        return BaseServiceMetadata.buildServiceKey(path, group, version);
    }
    public String toServiceStringWithoutResolving() {
        return buildString(true, false, false, true);
    }
    public String toServiceString() {
        return buildString(true, false, true, true);
    }
    @Deprecated
    public String getServiceName() {
        return getServiceInterface();