fix(@schematics/angular): don't overwrite target for specs

There's no need to.

Author: filipesilva

packages/schematics/angular/application/files/__sourcedir__/tsconfig.spec.json

@@ -4,7 +4,6 @@
     "outDir": "<%= sourcedir.split('/').map(x => '..').join('/') %>/out-tsc/spec",
     "baseUrl": "./",
     "module": "commonjs",
-    "target": "es5",
     "types": [
       "jasmine",
       "node"