Disable plugin if running Serverless <1.34.0 (#21)

Closes #20

README.md

@@ -3,6 +3,10 @@
 A [Serverless](https://serverless.com) plugin to add [IOpipe](https://www.iopipe.com)
 observability using [AWS Lambda Layers](https://docs.aws.amazon.com/lambda/latest/dg/configuration-layers.html) without requiring a code change.
 
+## Requirements
+
+* serverless >= 1.34.0
+
 ## Features
 
 * Supports Node.js and Python runtimes (more runtimes to come)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "serverless-iopipe-layers",
-  "version": "0.2.6",
+  "version": "0.2.7",
   "description": "Serverless plugin to add IOpipe lambda layers.",
   "main": "dist/index.js",
   "files": [
@@ -37,6 +37,7 @@
   "dependencies": {
     "fs-extra": "^7.0.1",
     "lodash": "^4.17.11",
+    "semver": "^6.1.1",
     "serverless": "^1.34.0"
   },
   "keywords": [

src/index.ts

@@ -2,6 +2,7 @@ import * as fs from "fs-extra";
 import * as path from "path";
 
 import * as _ from "lodash";
+import * as semver from "semver";
 import * as Serverless from "serverless";
 
 import * as layerArns from "./layers";
@@ -40,13 +41,23 @@ export default class IOpipeLayerPlugin {
   }
 
   public run() {
+    const version = this.serverless.getVersion();
+
+    if (semver.lt(version, "1.34.0")) {
+      this.serverless.cli.log(
+        `Serverless ${version} does not support layers. Please upgrade to >=1.34.0.`
+      );
+      return;
+    }
+
     const funcs = this.functions;
 
     Object.keys(funcs).forEach(funcName => {
       const funcDef = funcs[funcName];
       this.addLayer(funcName, funcDef);
     });
   }
+
   public cleanup() {
     this.removeNodeHelper();
   }

yarn.lock

@@ -1716,6 +1716,10 @@ semver@^5.0.3, semver@^5.1.0, semver@^5.3.0:
   version "5.6.0"
   resolved "https://registry.yarnpkg.com/semver/-/semver-5.6.0.tgz#7e74256fbaa49c75aa7c7a205cc22799cac80004"
 
+semver@^6.1.1:
+  version "6.1.1"
+  resolved "https://registry.yarnpkg.com/semver/-/semver-6.1.1.tgz#53f53da9b30b2103cd4f15eab3a18ecbcb210c9b"
+
 serverless-iopipe-layers@^0.2.1:
   version "0.2.1"
   resolved "https://registry.yarnpkg.com/serverless-iopipe-layers/-/serverless-iopipe-layers-0.2.1.tgz#dc192f2ef3cba789cb313e42bc26247802698b34"