Wrong type Option -> Result (#324)

Author: tesuji

.travis.yml

@@ -26,6 +26,7 @@ before_script:
   # NOTE: To increase caching efficiency, keep the same mdbook version
   # in blacksmith/Cargo.lock too
   - cargo install -v --debug --locked mdbook --vers '=0.3.6'
+  - cargo build --locked --manifest-path=blacksmith/Cargo.toml
 script:
   - mdbook build
   - cp website_config.json book/

blacksmith/src/main.rs

@@ -13,7 +13,7 @@ const CACHE_TTL_SECONDS: u64 = 3600; // 1 hour
 
 fn main() {
     // If RUST_LOG is present use that, else default to info level printing.
-    if let Some(v) = env::var("RUST_LOG") {
+    if let Ok(v) = env::var("RUST_LOG") {
         env_logger::init_from_env(v);
     } else {
         env_logger::builder()