docs[patch]: Fix minor typos (casing) in quickstart (#14138)

Fix casing of API and LangChain in the description text for the
LangServe example server.

docs/docs/get_started/quickstart.mdx

@@ -344,7 +344,7 @@ category_chain = chat_prompt | ChatOpenAI() | CommaSeparatedListOutputParser()
 app = FastAPI(
   title="LangChain Server",
   version="1.0",
-  description="A simple api server using Langchain's Runnable interfaces",
+  description="A simple API server using LangChain's Runnable interfaces",
 )
 
 # 3. Adding chain route