Compile error using strictNullChecks: true on branch v2.0

[mkoyamaRS]

Tried to use the alpha version in a project with the following tsconfig compile option
"strictNullChecks": true gives the following error

/node_modules/react-diff-viewer/lib/styles.d.ts
(3,5): Property 'diffContainer' of type 'string | undefined' is not assignable to string index type 'string'.

I did have a solution by changing the index signature of ReactDiffViewerStyles to [key: string]: string | undefined; - after changing this it compiles fine with the option.

[praneshr]

I feel it's okay to turn off the strictNullChecks