Fix error when single query is anonymous.

```
    "{\"query\":\"query {\\n  greeting(who: \\\"Tim\\\")\\n}\"}"
```
Notice that the query (immediately after the start of the JSON field
`query:`) has no operationName, i.e. it's anonymous.

This gets decoded to:
```
Just (GraphQLPostRequest {query = "query {\n  greeting(who: \"Tim\")\n}", operationName = "", variables = fromList []})
```
by a custom/temporary Aeson parser.

:blush: I didn't record it, and now it's gone. Something along the lines
of: `Just(Error{"query document error!definition error!query"})`
Not exactly, but that was the gist of it.

Realized that the parser might be choking on the absence of the
`operationName`, so tried to apply `optempty` to `nameParser` but Name
was not an instance of Monoid. Changed that and ¡viola! it worked
(sounds easy, but I learned something about applying Monoid to a newtype,
and also picked up a prior mistake where I forgot to import Data.Text).

On a side note, the 'custom/temporary' Aeson parser does not yet solve
the ambiguous `variables` problem mentioned here:
and here:
and obliquely here:

Author: sunwukonga

src/GraphQL/Internal/Name.hs

@@ -25,6 +25,7 @@ import Data.Text as T (Text)
 import qualified Data.Attoparsec.Text as A
 import Test.QuickCheck (Arbitrary(..), elements, listOf)
 import Data.String (IsString(..))
+import Data.Text as T (Text, append, empty)
 
 import GraphQL.Internal.Syntax.Tokens (tok)
 
@@ -35,6 +36,20 @@ import GraphQL.Internal.Syntax.Tokens (tok)
 -- https://facebook.github.io/graphql/#sec-Names
 newtype Name = Name { unName :: T.Text } deriving (Eq, Ord, Show)
 
+instance Monoid Name where
+    mempty  = Name T.empty
+--    mappend (Name {a}) mempty = Name {a}
+--    mappend mempty (Name {b}) = Name {b}
+    mappend (Name a1) (Name a2) = Name (T.append a1 a2)
+--    mappend = append
+--    mconcat = concat
+
+--newtype Any = Any { getAny :: Bool }
+
+--instance Monoid Any where
+--    mempty = Any False
+--    (Any b1) `mappend` (Any b2) = Any (b1 || b2)
+
 -- | Create a 'Name', panicking if the given text is invalid.
 --
 -- Prefer 'makeName' to this in all cases.

src/GraphQL/Internal/Syntax/Parser.hs

@@ -52,7 +52,7 @@ operationDefinition =
   <?> "operationDefinition error!"
 
 node :: Parser AST.Node
-node = AST.Node <$> nameParser
+node = AST.Node <$> optempty nameParser
                 <*> optempty variableDefinitions
                 <*> optempty directives
                 <*> selectionSet