Bump past removed version of croniter

The maintainer of croniter has unwisely unpublished version 0.3.27 (and
0.3.26) from PyPI in a misguided attempt to erase from history the
previous publishing of Bitcoin and Ethereum addresses through which they
wished to receive donations. (Described in the changelog only as
"history stripping (security)", but easily ascertained from the multiple
clones available.)

There are no substantive changes between 0.3.27 and 0.3.29, so just make
0.3.29 the upper constraint.

Change-Id: I2eb5968cc2e48fbfc157f37265989e5000d75a7f

upper-constraints.txt

@@ -106,7 +106,7 @@ pyinotify===0.9.6
 debtcollector===1.21.0
 requests-unixsocket===0.1.5
 asn1crypto===0.24.0
-croniter===0.3.27
+croniter===0.3.29
 octavia-lib===1.1.1
 python-watcherclient===2.2.0
 MarkupSafe===1.1.1