Fix registry description for settling velocity of bin 5

[jordanschnell]

This updates the registry description for settling velocity of bin 5 for GOCART

TYPE: text only

KEYWORDS: GOCART settling, description of bin 5 settling

SOURCE: encyclica

DESCRIPTION OF CHANGES:
Updated the registry to correct tezxt

Solution:
Text change

ISSUE: For use when this PR closes an issue.
Fixes #1982

LIST OF MODIFIED FILES:
M Registry/registry.chem

TESTS CONDUCTED:
None

RELEASE NOTE: Updates registry for variable description of settling velocity in bin 5

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None

[dudhia]

text change only