fix: pin tslib to 1.9.3

Author: greenkeeper[bot]

package.json

@@ -51,7 +51,7 @@
     "rollup-plugin-typescript2": "^0.16.1",
     "rollup-plugin-uglify": "^4.0.0",
     "standard-version": "^4.4.0",
-    "tslib": "^1.9.3",
+    "tslib": "1.9.3",
     "tslint": "^5.11.0",
     "typescript": "^3.0.1",
     "uglify-es": "^3.3.10"