Updating target in base tsconfig to be es2015 (#98)

Co-authored-by: Adam Cronin <acronin@backtrace.io>

Author: adamcronin42

tools/cli/tsconfig.json

@@ -3,7 +3,8 @@
     "compilerOptions": {
         "rootDir": "./src",
         "outDir": "./lib",
-        "composite": true
+        "composite": true,
+        "target": "es2020"
     },
     "exclude": ["node_modules", "tests", "lib"]
 }

tsconfig.base.json

@@ -1,6 +1,6 @@
 {
     "compilerOptions": {
-        "target": "es2020",
+        "target": "es2015",
         "module": "commonjs",
         "outDir": "./lib",
         "sourceMap": true,