fix(@angular-devkit/build-angular): update terser to 4.3.9 to address issue with keep_fnames

Closes #15996

Author: alan-agius4

packages/angular_devkit/build_angular/package.json

@@ -54,7 +54,7 @@
     "stylus": "0.54.5",
     "stylus-loader": "3.0.2",
     "tree-kill": "1.2.1",
-    "terser": "4.3.8",
+    "terser": "4.3.9",
     "terser-webpack-plugin": "1.4.1",
     "webpack": "4.39.2",
     "webpack-dev-middleware": "3.7.2",

yarn.lock

@@ -10203,16 +10203,7 @@ [email protected], terser-webpack-plugin@^1.4.1:
     webpack-sources "^1.4.0"
     worker-farm "^1.7.0"
 
-[email protected]:
-  version "4.3.8"
-  resolved "https://registry.yarnpkg.com/terser/-/terser-4.3.8.tgz#707f05f3f4c1c70c840e626addfdb1c158a17136"
-  integrity sha512-otmIRlRVmLChAWsnSFNO0Bfk6YySuBp6G9qrHiJwlLDd4mxe2ta4sjI7TzIR+W1nBMjilzrMcPOz9pSusgx3hQ==
-  dependencies:
-    commander "^2.20.0"
-    source-map "~0.6.1"
-    source-map-support "~0.5.12"
-
-terser@^4.1.2:
+[email protected], terser@^4.1.2:
   version "4.3.9"
   resolved "https://registry.yarnpkg.com/terser/-/terser-4.3.9.tgz#e4be37f80553d02645668727777687dad26bbca8"
   integrity sha512-NFGMpHjlzmyOtPL+fDw3G7+6Ueh/sz4mkaUYa4lJCxOPTNzd0Uj0aZJOmsDYoSQyfuVoWDMSWTPU3huyOm2zdA==