incorrect automatically named `FullJoin -on -eq`

Based on feature #43

Actual:
```PowerShell
1,2,3 | FullJoin 2,3,4 -On Left -eq Right

Left Right
---- -----
   1     1
   2     2
   3     3
   4     4
```

Expected:
```PowerShell
1,2,3 | FullJoin 2,3,4 -On Left -eq Right

Left Right
---- -----
   1
   2     2
   3     3
         4
```