Add sitemap generation

package-lock.json

@@ -9492,6 +9492,26 @@
         }
       }
     },
+    "gatsby-plugin-sitemap": {
+      "version": "2.2.8",
+      "resolved": "https://registry.npmjs.org/gatsby-plugin-sitemap/-/gatsby-plugin-sitemap-2.2.8.tgz",
+      "integrity": "sha512-FDWspoz4cymHis6d+PrDWm4RudoVHcGT1sjoiL8/i/zKaFZCVyDmxK2JDAy6TdpK4nLr/wc+np4n+Y5lKgfDRw==",
+      "dev": true,
+      "requires": {
+        "@babel/runtime": "^7.0.0",
+        "minimatch": "^3.0.4",
+        "pify": "^3.0.0",
+        "sitemap": "^1.13.0"
+      },
+      "dependencies": {
+        "pify": {
+          "version": "3.0.0",
+          "resolved": "https://registry.npmjs.org/pify/-/pify-3.0.0.tgz",
+          "integrity": "sha1-5aSs0sEB/fPZpNB/DbxNtJ3SgXY=",
+          "dev": true
+        }
+      }
+    },
     "gatsby-plugin-transition-link": {
       "version": "1.12.4",
       "resolved": "https://registry.npmjs.org/gatsby-plugin-transition-link/-/gatsby-plugin-transition-link-1.12.4.tgz",
@@ -18843,6 +18863,16 @@
       "integrity": "sha512-SbEG75TzH8G7eVXFSN5f9EExILKfly7SUvVY5DhhYLvfhKqhDFY0OzevWa/zwak0RLRfWS5AvfMWpd9gJvr5Yg==",
       "dev": true
     },
+    "sitemap": {
+      "version": "1.13.0",
+      "resolved": "https://registry.npmjs.org/sitemap/-/sitemap-1.13.0.tgz",
+      "integrity": "sha1-Vpy+IYAgKSamKiZs094Jyc60P4M=",
+      "dev": true,
+      "requires": {
+        "underscore": "^1.7.0",
+        "url-join": "^1.1.0"
+      }
+    },
     "slash": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/slash/-/slash-1.0.0.tgz",
@@ -20533,6 +20563,12 @@
       "integrity": "sha1-5z3T17DXxe2G+6xrCufYxqadUPo=",
       "dev": true
     },
+    "underscore": {
+      "version": "1.9.1",
+      "resolved": "https://registry.npmjs.org/underscore/-/underscore-1.9.1.tgz",
+      "integrity": "sha512-5/4etnCkd9c8gwgowi5/om/mYO5ajCaOgdzj/oW+0eQV9WxKBDZw5+ycmKmeaTXjInS/W0BzpGLo2xR2aBwZdg==",
+      "dev": true
+    },
     "underscore.string": {
       "version": "3.3.5",
       "resolved": "https://registry.npmjs.org/underscore.string/-/underscore.string-3.3.5.tgz",
@@ -20962,6 +20998,12 @@
         }
       }
     },
+    "url-join": {
+      "version": "1.1.0",
+      "resolved": "https://registry.npmjs.org/url-join/-/url-join-1.1.0.tgz",
+      "integrity": "sha1-dBxsL0WWxIMNZxhGCSDQySIC3Hg=",
+      "dev": true
+    },
     "url-loader": {
       "version": "1.1.2",
       "resolved": "https://registry.npmjs.org/url-loader/-/url-loader-1.1.2.tgz",