Fix bashism in Makefile
Fix bashism in Makefile

The [[ operator is a bashism, and fails with POSIX shells (such as dash),
replace it with a simplier version that does the same thing, without the
unnecessary $(shell) nesting.

kxepal/couchdb-documentation,kxepal/couchdb-documentation,kxepal/couchdb-documentation,cloudant/couchdb-documentation,cloudant/couchdb-documentation