Update @material-ui/pickers requirement from ^3.1.1 to ^3.2.0 in /docs (#32)

Updates the requirements on [@material-ui/pickers](https://github.com/mui-org/material-ui-pickers) to permit the latest version.
- [Release notes](https://github.com/mui-org/material-ui-pickers/releases)
- [Commits](mui/material-ui-pickers@v3.1.1...v3.2.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

docs/package.json

@@ -24,7 +24,7 @@
     "@material-ui/docs": "^4.0.0-beta.0",
     "@material-ui/icons": "^4.2.1",
     "@material-ui/lab": "^4.0.0-alpha.18",
-    "@material-ui/pickers": "^3.1.1",
+    "@material-ui/pickers": "^3.2.0",
     "@material-ui/styles": "^4.1.2",
     "@material-ui/system": "^4.3.0",
     "@trendmicro/react-interpolate": "^0.5.5",