Added the underscore node_module.

node_modules/underscore/cjs/_flatten.js

@@ -0,0 +1,33 @@
+var _getLength = require('./_getLength.js');
+var _isArrayLike = require('./_isArrayLike.js');
+var isArray = require('./isArray.js');
+var isArguments = require('./isArguments.js');
+
+// Internal implementation of a recursive `flatten` function.
+function flatten(input, depth, strict, output) {
+  output = output || [];
+  if (!depth && depth !== 0) {
+    depth = Infinity;
+  } else if (depth <= 0) {
+    return output.concat(input);
+  }
+  var idx = output.length;
+  for (var i = 0, length = _getLength(input); i < length; i++) {
+    var value = input[i];
+    if (_isArrayLike(value) && (isArray(value) || isArguments(value))) {
+      // Flatten current level of array or arguments object.
+      if (depth > 1) {
+        flatten(value, depth - 1, strict, output);
+        idx = output.length;
+      } else {
+        var j = 0, len = value.length;
+        while (j < len) output[idx++] = value[j++];
+      }
+    } else if (!strict) {
+      output[idx++] = value;
+    }
+  }
+  return output;
+}
+
+module.exports = flatten;