Compile as ES5 ?

[kevinLB]

Hello, would it be possible to have a build in ES5 ? Because it breaks on IE11 when I use it. I forked the branch to make the change in the "tsconfig.json" file in the meantime.

Note: There are errors and warnings during transpilation

> tsc -p . --newLine lf

src/index.ts:20:14 - error TS2585: 'Promise' only refers to a type, but is being used as a value here. Do you need to change your target library? Try changing the `lib` compiler option to es2015 or later.

20       return Promise.all(
                ~~~~~~~

src/index.ts:27:69 - error TS7031: Binding element 'key' implicitly has an 'any' type.

27       const dataStorage = dataWithKeys.reduce((previousValue: any, [key, data]) => {
                                                                       ~~~

src/index.ts:27:74 - error TS7031: Binding element 'data' implicitly has an 'any' type.

27       const dataStorage = dataWithKeys.reduce((previousValue: any, [key, data]) => {
                                                                            ~~~~

src/storage-sync.ts:60:31 - error TS2339: Property 'assign' does not exist on type 'ObjectConstructor'.

60                 return Object.assign({}, acc, {
                                 ~~~~~~

Thanks :)