workaround for typescript 1.1 incompatibility

the build tool currently installs the latest typescript version.
compilation with typescript 1.1 (released on oct 6) fails with to the following error:
```
$ tools/gup compile
gup  compile
gup    schemas/inputs
gup    shellshape/all
gup      shellshape/extension.js
gup        shellshape/_sources
../src/workspace.ts(434,10): error TS2365: Operator '===' cannot be applied to types 'Window' and 'Window'.
gup      Target `shellshape/extension.js` failed with exit status 1
gup    Target `shellshape/all` failed with exit status 2
gup  Target `compile` failed with exit status 2
```
this patch forces the installation of an older typescript version which works correctly