Use ? operator replace unwrap to handle error

[chikaku]

before:

$ ./target/release/servicer create index.js
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: "index.js is not a file"', src/main.rs:172:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

after:

$ ./target/release/servicer create index.js
Error: "index.js is not a file"

[secretshardul]

Agree that the errors are untidy but line numbers help with debugging (#1). Let's attain more stability then we can merge this PR.

[secretshardul]

Merged in v0.1.4