"054-nvd3-line-chart-output": Add additional sleep

[MadhulikaTanuboddi]

On Windows builds (esp Win R 4.1 and 3.5), this test has been failing due to the timing issue with the first snapshot (immediately after setting the custom window size with app$setWindowSize(1100, 750))

Added a sleep to fix this.

[schloerke]

Clean checks. Merging