minor update to multizip documentation

[bsubei]

The docs for multizip() refer to it as a macro, even though it is clearly a function. I'm guessing this typo originated from the copy-paste from izip!(), which has a similar section noting the result:

from multizip():

/// **Note:** The result of this macro is a value of a named type (`Zip<(I, J,

from izip!():

/// **Note:** The result of this macro is in the general case an iterator

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.52%. Comparing base (6814180) to head (cf08680).
Report is 18 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #882      +/-   ##
==========================================
+ Coverage   94.38%   94.52%   +0.13%     
==========================================
  Files          48       48              
  Lines        6665     6574      -91     
==========================================
- Hits         6291     6214      -77     
+ Misses        374      360      -14     

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