Update spec for the memop binary format change (#33)

Author: rossberg

document/core/binary/instructions.rst

@@ -198,7 +198,7 @@ Each variant of :ref:`memory instruction <syntax-instr-memory>` is encoded with
    \production{memory argument} & \Bmemarg &::=&
      a{:}\Bu32~~o{:}\Bu32 &\Rightarrow& 0~\{ \ALIGN~a,~\OFFSET~o \}
        & (\iff a < 2^6) \\ &&|&
-     a{:}\Bu32~~o{:}\Bu32~~x{:}\memidx &\Rightarrow& x~\{ \ALIGN~(a - 2^6),~\OFFSET~o \}
+     a{:}\Bu32~~x{:}\memidx~~o{:}\Bu32 &\Rightarrow& x~\{ \ALIGN~(a - 2^6),~\OFFSET~o \}
        & (\iff 2^6 \leq a < 2^7) \\
    \production{instruction} & \Binstr &::=& \dots \\ &&|&
      \hex{28}~~m{:}\Bmemarg &\Rightarrow& \I32.\LOAD~m \\ &&|&