define 4 bytes for FieldDef

doc/r1cs_bin_format.md

@@ -152,9 +152,9 @@ Size in bytes of the section
 
 Section Type: 0x01
 ````
-     ┏━━━━┳━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
-     ┃ 4  │  FieldDefSize   ┃  FieldDef                    ┃      field Id
-     ┗━━━━┻━━━━━━━━━━━━━━━━━┻━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
+     ┏━━━━┳━━━━━━━━━━━━━━━━━┳━━━┳━━━━━━━━━┳━━━━━━━━━━━━━━━━┓
+     ┃ 4  │  FieldDefSize   ┃ 4 ┃FieldDef ┃    field Id    ┃
+     ┗━━━━┻━━━━━━━━━━━━━━━━━┻━━━┻━━━━━━━━━┻━━━━━━━━━━━━━━━━┛
      ┏━━━━┳━━━━━━━━━━━━━━━━━┓
      ┃ 4  │   00 00 00 00   ┃        bigInt Format
      ┗━━━━┻━━━━━━━━━━━━━━━━━┛
@@ -501,7 +501,7 @@ The format will be:
 
 ````
      ┏━━━━━━━━━━━━━━┓
-     ┃ 72 31 63 77  ┃        Magic
+     ┃ 72 31 63 73  ┃        Magic
      ┣━━━━━━━━━━━━━━┫
      ┃ 01 00 00 00  ┃       Version
      ┣━━━━━━━━━━━━━━┫