Add unit test to get coverage over 90%.

    +-----------------------------------------+-----------+-----------+-----------+-----------+
    | File                                    |   % Stmts |% Branches |   % Funcs |   % Lines |
    +-----------------------------------------+-----------+-----------+-----------+-----------+
    |    gallery-charts-stockindicators/      |     90.12 |     66.17 |     94.41 |     90.12 |
    |       gallery-charts-stockindicators.js |     90.12 |     66.17 |     94.41 |     90.12 |
    +-----------------------------------------+-----------+-----------+-----------+-----------+
    | All files                               |     90.12 |     66.17 |     94.41 |     90.12 |
    +-----------------------------------------+-----------+-----------+-----------+-----------+

	modified:   tests/unit/assets/charts-stockindicators-tests.js
	new file:   tests/unit/assets/gridlines-canvas-stockindicators-tests.js
	new file:   tests/unit/assets/gridlines-stockindicators-tests.js
	modified:   tests/unit/assets/mockconfig.js
	new file:   tests/unit/assets/spark-stockindicators-tests.js
	new file:   tests/unit/gridlines-canvas-stockindicators.html
	new file:   tests/unit/gridlines-stockindicators.html
	new file:   tests/unit/spark-stockindicators.html