Fix erroneous argument in __len__ definition for Namespace.

[cjcscott]

Fixes a small bug in the __len__ definition for namespace.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (089db65) 99.56% compared to head (982761c) 99.56%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #29 +/- ## ======================================= Coverage 99.56% 99.56% ======================================= Files 54 54 Lines 85708 85708 Branches 817 817 ======================================= Hits 85333 85333 Misses 249 249 Partials 126 126 ``` | [Files Changed](https://app.codecov.io/gh/BoothGroup/ebcc/pull/29?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BoothGroup) | Coverage Δ | | |---|---|---| | [ebcc/util.py](https://app.codecov.io/gh/BoothGroup/ebcc/pull/29?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=BoothGroup#diff-ZWJjYy91dGlsLnB5) | `70.44% <100.00%> (ø)` | |

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[obackhouse]

Ta