Update a_star.py

[rezaxdi]

Typo fix in function name

[coveralls]

Pull Request Test Coverage Report for Build 766

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 102 unchanged lines in 16 files lost coverage.
• Overall coverage decreased (-1.2%) to 90.161%

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Files with Coverage Reduction	New Missed Lines	%
PathPlanning/FrenetOptimalTrajectory/cubic_spline_planner.py	1	70.71%
PathPlanning/DynamicWindowApproach/dynamic_window_approach.py	1	88.98%
PathPlanning/RRT/simple_rrt.py	3	93.06%
tests/test_dynamic_window_approach.py	4	75.0%
tests/test_histogram_filter.py	4	76.47%
tests/test_batch_informed_rrt_star.py	4	75.0%
tests/test_fast_slam2.py	4	76.47%
tests/test_frenet_optimal_trajectory.py	4	77.78%
tests/test_fast_slam1.py	4	76.47%
tests/test_a_star.py	4	73.33%

Totals
Change from base Build 765:	-1.2%
Covered Lines:	6488
Relevant Lines:	7196

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💛 - Coveralls

[AtsushiSakai]

@rezaxdi Thank you!!