Stochastic test failure

[leeping]

Lately I've noticed an stochastic failure of one of my unit tests. I think this is due to the TINKER version update and their geometry optimization code being changed, but I can't prove it.

	 >	test_engine.TestAmber99SB.test_optimized_geometries
	 >	
	 >	Traceback (most recent call last):
	 >	  File "/home/travis/miniconda/envs/forcebalance_env/lib/python2.7/unittest/case.py", line 329, in run
	 >	    testMethod()
	 >	  File "test/test_engine.py", line 139, in test_optimized_geometries
	 >	  File "/home/travis/miniconda/envs/forcebalance_env/lib/python2.7/unittest/case.py", line 561, in assertAlmostEqual
	 >	    raise self.failureException(msg)
	 >	AssertionError: -61.8518871 != -61.820866873804967 within 0.001 delta : TINKER optimized energies do not match the reference```