EditPDF: Fix typo in name of property of editor class

Prerequisites: You need a course, with an assignment and one student enrolled. Test steps (shape/line/highlighter tools - Regression test only): Select the Line tool Draw a line using the tool Change the tool colour only, and then draw another line. Confirm that you now have 2 different coloured lines and that the line tool is still selected. Now, select the rectangle tool Change the tool colour. The tool may change back to line. This is due to an existing bug ( MDL-56364 ). Re-select the rectangle tool. Draw a rectangle on the page and confirm that it uses the new colour. Test steps (comments and stamps - Regression test only): Select the comment tool and create a comment using the selected colour. Change the comment colour and confirm that the comment tool is still selected Create another comment and confirm that the colour is the one you just picked Try having the rectangle tool selected and then changing the comment colour. Confirm that after changing the comment colour, the comment tool is automatically selected. Select the stamp tool and create a stamp using the selected stamp type Change the stamp type and confirm that the stamp tool is still selected Create another stamp and confirm that the colour is the one you just picked Try having the rectangle tool selected and then changing the stamp type. Confirm that after changing the stamp type, the stamp tool is automatically selected.