rust: bump bitflags dependency version

So that lexical-core, needed by nom, and using bitflags
is used with version 0.7.5 instead of version 0.7.0
which fixed the fact that BITS is now a reserved keyword
in nightly version

rust/Cargo.toml.in

@@ -21,7 +21,7 @@ function-macro = []
 
 [dependencies]
 nom = "~5.1.2"
-bitflags = "~1.0.4"
+bitflags = "~1.2.1"
 byteorder = "~1.4.2"
 uuid = "~0.8.2"
 crc = "~1.8.1"