Pinning to patch-updates only for react-native and react-native-svg

[marzolfb]

After attempting to upgrade to newer versions of react-native-svg (and also react-native), I found rendering problems on the charts in the example app:

• When switching to react-native-svg 4.6.1 and react-native 0.40.0, a number of charts replace the (blue colored) grid lines with bold black lines and the radar chart didn't render some of its (blue) lines at all
• Switching to react-native-svg 5.14 (also using react-native 0.40.0), all of the chart problems above are fixed but then the bar chart is missing its labels due to a new text rotation bug in react-native-svg - Text translating/rendering x/y incorrectly when rotate > 0 from release 5.0.2+ software-mansion/react-native-svg#242

Also, unfortunately we are using caret semver ranges in package.json for both react-native and react-native-svg which means that a person cloning this project and doing an npm install in the example app for the first time will pull react-native-svg version 4.6.1 rather than 4.4.1. Using tilde ranges will help pin updates on these two key dependencies to patch-level-only updates. This addresses #55 and eliminates the need for extra steps to work around it