fix: broken link to metrics (#311)

Closes #293

Author: Younes

docs/howtos/integrations/langchain.ipynb

@@ -126,7 +126,7 @@
    "source": [
     "## Introducing `RagasEvaluatorChain`\n",
     "\n",
-    "`RagasEvaluatorChain` creates a wrapper around the metrics ragas provides (documented [here](https://github.com/explodinggradients/ragas/blob/main/docs/metrics.md)), making it easier to run these evaluation with langchain and langsmith.\n",
+    "`RagasEvaluatorChain` creates a wrapper around the metrics ragas provides (documented [here](https://github.com/explodinggradients/ragas/blob/main/docs/concepts/metrics/index.md)), making it easier to run these evaluation with langchain and langsmith.\n",
     "\n",
     "The evaluator chain has the following APIs\n",
     "\n",