Issue 665: pin es6-module-transpiler at 0.3.3 with npm-shrinkwrap

Issue #665: handlebars build is broken with es6-module-transpiler v0.3.4
(also see square/es6-module-transpiler#81 and square/es6-module-transpiler#82)

This PR adds npm-shrinkwrap.json, to pin dependecies to desired versions (such as 0.3.3 of es6-module-transpiler),