fix(ci): pin proc-macro2 to MSRV supported 1.0.103

Author: oleonardolima

.github/workflows/cont_integration.yml

@@ -75,6 +75,7 @@ jobs:
         cargo update -p itoa --precise "1.0.15"
         cargo update -p serde_json --precise "1.0.145"
         cargo update -p ryu --precise "1.0.20"
+        cargo update -p proc-macro2 --precise "1.0.103"
 
         cargo update -p bzip2-sys --precise "0.1.12+1.0.8" # dev-dependency
     - name: Build

README.md

@@ -44,4 +44,5 @@ cargo update -p log --precise "0.4.28"
 cargo update -p itoa --precise "1.0.15"
 cargo update -p serde_json --precise "1.0.145"
 cargo update -p ryu --precise "1.0.20"
+cargo update -p proc-macro2 --precise "1.0.103"
 ```