Remove mocha type reference in @opencensus/core release code

[draffensperger]

The generated code in build/src/trace/model/tracer.d.ts and build/src/trace/model/types.d.ts includes a line /// <reference types="mocha" />. I believe that's because TypeScript sees that the NodeJS.EventEmitter type is not defined in the file and so it pulls in the included global types, including the Mocha types. That means that when @opencensus/core is imported into another TypeScript NPM module, it needs to bring in the @types/mocha package in order to compile.

This fixes that by separating out the test and release compilation steps and having two separate tsconfig files with different types definitions. As a side benefit, this also means that npm run prepare will fail if any code in the src folder accidentally references any Mocha types.

[codecov-io]

Codecov Report

Merging #254 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #254   +/-   ##
=======================================
  Coverage   94.61%   94.61%           
=======================================
  Files         101      101           
  Lines        7312     7312           
  Branches      690      690           
=======================================
  Hits         6918     6918           
  Misses        394      394

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[draffensperger]

This will enable use of Jasmine for unit tests in the opencensus-web project that I'm thinking will make use of the TypeScript interfaces from @opencensus/core. See census-instrumentation/opencensus-web#2

[justindsmith]

LGTM