Fix incorrect usage of rspec raise_error

WARNING: Using `expect { }.not_to raise_error(SpecificErrorClass)`
 risks false positives, since literally any other error would cause
 the expectation to pass, including those raised by Ruby
 (e.g. NoMethodError, NameError and ArgumentError), meaning the code
 you are intending to test may not even get reached. Instead consider
 using `expect { }.not_to raise_error` or
 `expect { }.to raise_error(DifferentSpecificErrorClass)`.

spec/faraday/error_spec.rb

@@ -53,7 +53,7 @@
       end
 
       it 'allows backward-compatible class to be subclassed' do
-        expect { class CustomError < Faraday::Error::ClientError; end }.not_to raise_error(TypeError)
+        expect { class CustomError < Faraday::Error::ClientError; end }.not_to raise_error
       end
     end