regenerated @azure/arm-timeseriesinsights to fix polymorphic mapper lookup issues

[amarzavery]

amarz-MBP:azure-sdk-for-js amarz$ gulp codegen --azure-rest-api-specs-root "/Users/amarz/sdk/azure-rest-api-specs" --use "/Users/amarz/sdk/autorest.typescript" --package "@azure/arm-timeseriesinsights"
[15:09:11] Requiring external module ts-node/register
(node:53574) ExperimentalWarning: The fs.promises API is experimental
[15:09:12] Using gulpfile ~/sdk/azure-sdk-for-js/gulpfile.ts
[15:09:12] Starting 'codegen'...
Passed arguments: codegen, --azure-rest-api-specs-root, /Users/amarz/sdk/azure-rest-api-specs, --use, /Users/amarz/sdk/autorest.typescript, --package, @azure/arm-timeseriesinsights
>>>>>>>>>>>>>>>>>>> Start: "["@azure/arm-timeseriesinsights"]" >>>>>>>>>>>>>>>>>>>>>>>>>
Executing command:
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autorest --typescript --typescript-sdks-folder=/Users/amarz/sdk/azure-sdk-for-js --license-header=MICROSOFT_MIT_NO_VERSION /Users/amarz/sdk/azure-rest-api-specs/specification/timeseriesinsights/resource-manager/readme.md --use=/Users/amarz/sdk/autorest.typescript
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AutoRest code generation utility [version: 2.0.4283; node: v10.15.3]
(C) 2018 Microsoft Corporation.
https://aka.ms/autorest
   Loading AutoRest core      '/Users/amarz/.autorest/@[email protected]/node_modules/@microsoft.azure/autorest-core/dist' (2.0.4387)
   Loading local AutoRest extension '@microsoft.azure/autorest.typescript' (/Users/amarz/sdk/autorest.typescript)
   Loading AutoRest extension '@microsoft.azure/autorest.modeler' (2.3.51->2.3.51)
INFORMATION: Getting the package version from the pre-existing package.json file in the output folder.
INFORMATION: Got version "1.2.0" for package "@azure/arm-timeseriesinsights" from existing package.json file.

• fixes Nested Polymorphism and Discriminators autorest.typescript#458