“accumulator”→“previousValue” in array-reduce.js live example (#1887)
“accumulator”→“previousValue” in array-reduce.js live example (#1887)

For consistency with https://github.com/mdn/content/commit/260094b
changes (https://github.com/mdn/content/pull/7484), this change replaces
the variable name “accumulator” with “previousValue” in the
live-examples/js-examples/array/array-reduce.js live-example source.
mdn/interactive-examples,mdn/interactive-examples,mdn/interactive-examples