typescript: do not lint lib/* and do coverage with sourcemaps

- do not lint build directory lib/*
- output source maps from typescript files for coverage testing
- fix a istanbul ignore in fetch.ts

.eslintignore

@@ -1,3 +1,4 @@
 /node_modules/
-/build/
+/build/airtable.browser.js
 /test/test_files/airtable.browser.js
+/lib/

src/base.ts

@@ -18,8 +18,8 @@ const userAgent = `Airtable.js/${packageVersion}`;
 type BaseRequestOptions = {
     method?: string;
     path?: string;
-    qs?: {};
-    headers?: {};
+    qs?: any;
+    headers?: any;
     body?: any;
     _numAttempts?: number;
 };

src/fetch.ts

@@ -1,4 +1,6 @@
 import nodeFetch from 'node-fetch';
 
-// istanbul ignore next
-export = typeof window === 'undefined' ? (nodeFetch as typeof fetch) : fetch;
+export = (
+    // istanbul ignore next
+    typeof window === 'undefined' ? (nodeFetch as typeof fetch) : fetch
+);

tsconfig.json

@@ -6,7 +6,8 @@
         "esModuleInterop": true,
         "outDir": "lib",
         "noImplicitAny": false,
-        "strict": false
+        "strict": false,
+        "sourceMap": true
     },
     "include": ["src/**/*.ts", "src/internal_config.json"]
 }