build(deps-dev): update eslint-loader to ^3

eslint-loader is the last version to [support both ESLint 5 and 6](https://github.com/webpack-contrib/eslint-loader/blob/v3.0.4/package.json#L40).

Given the [changelog for v3.0.0](https://github.com/webpack-contrib/eslint-loader/blob/master/CHANGELOG.md#300-2019-08-24), the only breaking changes are:
- drop support for Node < 8.9.0 (we did it too symfony#731)
- minimum supported webpack version is 4: not a problem
- minimum supported eslint version is 5: not a problem

package.json

@@ -67,7 +67,7 @@
     "chai-subset": "^1.6.0",
     "core-js": "^3.0.0",
     "eslint": "^5.15.2",
-    "eslint-loader": "^2.1.2",
+    "eslint-loader": "^3.0.0",
     "eslint-plugin-header": "^1.0.0",
     "eslint-plugin-import": "^2.8.0",
     "eslint-plugin-node": "^8.0.1",

yarn.lock

@@ -3140,16 +3140,16 @@ eslint-import-resolver-node@^0.3.2:
     debug "^2.6.9"
     resolve "^1.13.1"
 
-eslint-loader@^2.1.2:
-  version "2.2.1"
-  resolved "https://registry.yarnpkg.com/eslint-loader/-/eslint-loader-2.2.1.tgz#28b9c12da54057af0845e2a6112701a2f6bf8337"
-  integrity sha512-RLgV9hoCVsMLvOxCuNjdqOrUqIj9oJg8hF44vzJaYqsAHuY9G2YAeN3joQ9nxP0p5Th9iFSIpKo+SD8KISxXRg==
+eslint-loader@^3.0.0:
+  version "3.0.4"
+  resolved "https://registry.yarnpkg.com/eslint-loader/-/eslint-loader-3.0.4.tgz#4329482877e381c91460a055bcd08d3855b9922d"
+  integrity sha512-I496aBd+Hi23Y0Cx+sKvw+VwlJre4ScIRlkrvTO6Scq68X/UXbN6F3lAhN8b0Zv8atAyprkyrA42K5QBJtCyaw==
   dependencies:
-    loader-fs-cache "^1.0.0"
-    loader-utils "^1.0.2"
-    object-assign "^4.0.1"
-    object-hash "^1.1.4"
-    rimraf "^2.6.1"
+    fs-extra "^8.1.0"
+    loader-fs-cache "^1.0.3"
+    loader-utils "^1.2.3"
+    object-hash "^2.0.3"
+    schema-utils "^2.6.5"
 
 eslint-module-utils@^2.4.1:
   version "2.6.0"
@@ -5032,7 +5032,7 @@ load-json-file@^2.0.0:
     pify "^2.0.0"
     strip-bom "^3.0.0"
 
-loader-fs-cache@^1.0.0:
+loader-fs-cache@^1.0.3:
   version "1.0.3"
   resolved "https://registry.yarnpkg.com/loader-fs-cache/-/loader-fs-cache-1.0.3.tgz#f08657646d607078be2f0a032f8bd69dd6f277d9"
   integrity sha512-ldcgZpjNJj71n+2Mf6yetz+c9bM4xpKtNds4LbqXzU/PTdeAX0g3ytnU1AJMEcTk2Lex4Smpe3Q/eCTsvUBxbA==
@@ -5750,10 +5750,10 @@ object-copy@^0.1.0:
     define-property "^0.2.5"
     kind-of "^3.0.3"
 
-object-hash@^1.1.4:
-  version "1.3.1"
-  resolved "https://registry.yarnpkg.com/object-hash/-/object-hash-1.3.1.tgz#fde452098a951cb145f039bb7d455449ddc126df"
-  integrity sha512-OSuu/pU4ENM9kmREg0BdNrUDIl1heYa4mBZacJc+vVWz4GtAwu7jO8s4AIt2aGRUTqxykpWzI3Oqnsm13tTMDA==
+object-hash@^2.0.3:
+  version "2.0.3"
+  resolved "https://registry.yarnpkg.com/object-hash/-/object-hash-2.0.3.tgz#d12db044e03cd2ca3d77c0570d87225b02e1e6ea"
+  integrity sha512-JPKn0GMu+Fa3zt3Bmr66JhokJU5BaNBIh4ZeTlaCBzrBsOeXzwcKKAK1tbLiPKgvwmPXsDvvLHoWh5Bm7ofIYg==
 
 object-inspect@^1.7.0:
   version "1.7.0"