fix legacy warning for ENV APP_DIR by including '=' #2049 #6457

Job	Run time
Tests (mysql, rails test test/unit)	26m 1s
Tests (mysql, rails test test/functional)	35m 43s
Tests (mysql, rails test test/integration)	17m 15s
Tests (mysql, rspec spec)	3m 26s
Tests (mysql, rake assets:precompile)	3m 20s
Tests (mysql, rake db:setup)	3m 40s
Tests (mysql, rake db:migrate)	3m 24s
Tests (mysql, rake seek:upgrade)	3m 28s
Tests (sqlite3, rails test test/unit)	20m 21s
	1h 56m 38s

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