fix: update core istanbul libraries (#426)

Author: bcoe

package.json

@@ -83,10 +83,10 @@
     "glob": "^7.0.6",
     "istanbul-lib-coverage": "^1.0.0",
     "istanbul-lib-hook": "^1.0.0-alpha.4",
-    "istanbul-lib-instrument": "^1.1.3",
+    "istanbul-lib-instrument": "^1.2.0",
     "istanbul-lib-report": "^1.0.0-alpha.3",
     "istanbul-lib-source-maps": "^1.0.2",
-    "istanbul-reports": "^1.0.0-alpha.8",
+    "istanbul-reports": "^1.0.0",
     "md5-hex": "^1.2.0",
     "micromatch": "^2.3.11",
     "mkdirp": "^0.5.0",