[ISSUE #4416] Update dledger version to 0.2.6

[RongtongJin]

Make sure set the target branch to develop

What is the purpose of the change

Update dledger version to 0.2.6

Brief changelog

XX

Verifying this change

XXXX

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[coveralls]

Coverage increased (+0.05%) to 52.168% when pulling 6e35b4f on RongtongJin:develop_3 into 9ceff5c on apache:develop.