Update SPEC.md & => ? (#217)

Author: mahnunchik

SPEC.md

@@ -92,7 +92,7 @@ solana:mvines9iiHiQTysrwkJjGf2gb9Ex9jXJX8ns3qwf2kN?amount=0.01&spl-token=EPjFWdd
 
 ##### URL describing a transfer request for SOL. The user must be prompted for the amount.
 ```
-solana:mvines9iiHiQTysrwkJjGf2gb9Ex9jXJX8ns3qwf2kN&label=Michael
+solana:mvines9iiHiQTysrwkJjGf2gb9Ex9jXJX8ns3qwf2kN?label=Michael
 ```
 
 ## Specification: Transaction Request