### Describe Your Changes
If a dict flag has only one value without a prefix it is supposed to
replace default value.
Previously, when flag was set to `-flag=2` and the default value in
`NewDictInt` was set to 1 the resulting value for any `flag.Get()` call
would be 1 which is not expected.
This commit updates default value for the flag in case there is only one
entry for flag and the entry is a number without a key.
This affects cluster version and specifically `replicationFactor` flag
usage with vmstorage [node
groups](https://docs.victoriametrics.com/cluster-victoriametrics/#vmstorage-groups-at-vmselect).
Previously, the following configuration would effectively be ignored:
```
/path/to/vmselect \
-replicationFactor=2 \
-storageNode=g1/host1,g1/host2,g1/host3 \
-storageNode=g2/host4,g2/host5,g2/host6 \
-storageNode=g3/host7,g3/host8,g3/host9
```
Changes from this PR will force default value for `replicationFactor`
flag to be set to `2` which is expected as the result of this
configuration.
---------
Signed-off-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>
