inform user about bundler problem #283

Job	Run time
Apache2 tests on Linux	2m 28s
C++ tests on Linux	1m 27s
Apache2 tests on macOS	2m 38s
C++ tests on macOS	4m 25s
Homebrew packaging tests	8m 7s
Nginx tests on Linux	2m 9s
Nginx dynamic module tests on Linux	1m 6s
Nginx tests on macOS	3m 1s
Nginx dynamic module tests on macOS	1m 31s
Node.js tests on Linux	21s
Ruby tests on Linux	1m 7s
Node.js tests on macOS	24s
Ruby tests on macOS	1m 1s
Source packaging tests	33s
Passenger Standalone tests on Linux	3m 36s
Passenger Standalone tests on macOS	3m 59s
	37m 53s

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