fix data manipulation for download graph

[TyOverby]

No description provided.

[frewsxcv]

not ok 19 PhantomJS 1.9 - JSCS - components/download-graph.js: should pass jscs
    ---
        actual: >
            false
        expected: >
            true
        stack: >
                at http://localhost:7357/assets/test-support.js:3357
                at http://localhost:7357/assets/tests.js:225
                at runTest (http://localhost:7357/assets/test-support.js:2662)
                at http://localhost:7357/assets/test-support.js:2647
                at http://localhost:7357/assets/test-support.js:2810
                at process (http://localhost:7357/assets/test-support.js:2486)
                at begin (http://localhost:7357/assets/test-support.js:2468)
                at http://localhost:7357/assets/test-support.js:3238
        message: >
            components/download-graph.js should pass jscs.
            disallowSpaceBeforeSemicolon: Illegal space before semicolon at components/download-graph.js :
                33 |            // End before the last element is reached because we never
                34 |            // want to change the last element.
                35 |            for (let i = 1; i < data.length - 1 ; i++) {
            -------------------------------------------------------^
                36 |                // k + 1 because the first entry in the array is the date
                37 |                let value = data[i][k];
        Log: |
    ...

[alexcrichton]

Thanks @TyOverby!