Raise rustc checked in build script to 1.48
diff --git a/build.rs b/build.rs
index 73c6228..ae3ef67 100644
--- a/build.rs
+++ b/build.rs
@@ -20,8 +20,8 @@
     }
 
     if let Some(rustc) = rustc_version() {
-        if rustc.minor < 43 {
-            println!("cargo:warning=The cxx crate requires a rustc version 1.43.0 or newer.");
+        if rustc.minor < 48 {
+            println!("cargo:warning=The cxx crate requires a rustc version 1.48.0 or newer.");
             println!(
                 "cargo:warning=You appear to be building with: {}",
                 rustc.version,