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

(cherry picked from commit 0105d4f017)

rust/Cargo.toml.in

@@ -21,7 +21,7 @@ decompression = ["flate2", "brotli"]
 
 [dependencies]
 nom = "= 5.1.1"
-bitflags = "1.0"
+bitflags = "~1.2.1"
 byteorder = "1.3"
 uuid = "0.8"
 crc = "1.8"