EKF-SLAM: Fix jacobian of observation

[m-dobler]

I believe the partial derivative of an observation with respect to the angle should be equal to -1, yet in the code it's currently -1/q.

Here is a source I could find on the topic:
http://ais.informatik.uni-freiburg.de/teaching/ws12/mapping/pdf/slam04-ekf-slam.pdf, Slide 33

Would greatly appreciate it if someone would take a second look!

[coveralls]

Pull Request Test Coverage Report for Build 1088

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.05%) to 90.385%

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Files with Coverage Reduction	New Missed Lines	%
PathPlanning/ClosedLoopRRTStar/pure_pursuit.py	1	96.12%
ArmNavigation/n_joint_arm_to_point_control/n_joint_arm_to_point_control.py	4	93.59%

Totals
Change from base Build 1087:	-0.05%
Covered Lines:	6731
Relevant Lines:	7447

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💛 - Coveralls

[AtsushiSakai]

@m-dobler Good catch!! I think you are right. Thank you!!