Fixed typo in stanley_controller.py

[Gjacquenot]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 1100

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 90.398%

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Files with Coverage Reduction	New Missed Lines	%
PathPlanning/BatchInformedRRTStar/batch_informed_rrtstar.py	1	81.41%

Totals
Change from base Build 1098:	0.04%
Covered Lines:	6722
Relevant Lines:	7436

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💛 - Coveralls

[AtsushiSakai]

@Gjacquenot Thanks!!