Update CHANGELOG for v20.07.0-rc2. (dgraph-io#1429)

(cherry picked from commit 21bda50)

Changelog for v20.07.0 (dgraph-io#1411)

(cherry picked from commit b5a5d66)

Fix release date for v2.0.3

Merge pull request dgraph-io#1273 from dgraph-io/ibrahim/release/v2.0…

…-cherry-pick-v2.0.3

Cherry-pick commits for v2.0.3

fix release date for v1.6.1

Fix release date for v1.6.1 (dgraph-io#1271)

Fix changelog for v2.0.2

Merge branch 'master' into HEAD

Update CHANGELOG for v2.0.1 release. (dgraph-io#1181)

(cherry picked from commit 23a73cd)

Rename option builder from WithInmemory to WithInMemory. (dgraph-io#1169

)

The name of the option builder func should be spelled the same as the
option name itself.

The godoc already has the func documented as "WithInMemory".