增加air默认配置

.air.toml

+root = "."
+testdata_dir = "testdata"
+tmp_dir = "bin"
+
+[build]
+bin = "./bin/cmd -conf configs/config.yaml"
+cmd = "go build -o bin/ ./..."
+delay = 200
+exclude_dir = ["assets", "tmp", "vendor", "testdata", "bin"]
+exclude_file = []
+exclude_regex = ["_test.go"]
+exclude_unchanged = false
+follow_symlink = false
+full_bin = ""
+include_dir = []
+include_ext = ["go", "tpl", "tmpl", "html"]
+kill_delay = 100
+log = "build-errors.log"
+send_interrupt = true
+stop_on_error = true
+
+[color]
+app = ""
+build = "yellow"
+main = "magenta"
+runner = "green"
+watcher = "cyan"
+
+[log]
+time = true
+
+[misc]
+clean_on_exit = false
+
+[screen]
+clear_on_rebuild = false