Bump to syn 0.15

cuviper · cuviper · commit 1dbcc5d3bacd · 2018-10-03T10:15:21.000-07:00
diff --git a/Cargo.toml b/Cargo.toml
@@ -16,7 +16,7 @@ build = "build.rs"
 num-traits = "0.2"
 proc-macro2 = "0.4.2"
 quote = "0.6"
-syn = "0.14"
+syn = "0.15"
 
 [dev-dependencies]
 num = "0.2"
