Update handlebars dependency (elastic#64402)

I only updated the direct dependency. There are a couple of
transitive dependencies which still resolve to older versions, but
these are sourced from devDependencies and not a priority to be
updated.

package.json

@@ -172,7 +172,7 @@
     "globby": "^8.0.1",
     "good-squeeze": "2.1.0",
     "h2o2": "^8.1.2",
-    "handlebars": "4.5.3",
+    "handlebars": "4.7.6",
     "hapi": "^17.5.3",
     "hjson": "3.1.0",
     "hoek": "^5.0.4",

x-pack/package.json

@@ -178,7 +178,7 @@
     "graphql-fields": "^1.0.2",
     "graphql-tag": "^2.9.2",
     "graphql-tools": "^3.0.2",
-    "handlebars": "4.5.3",
+    "handlebars": "4.7.6",
     "hapi-auth-cookie": "^9.0.0",
     "history": "4.7.2",
     "history-extra": "^4.0.2",

yarn.lock

@@ -10912,7 +10912,7 @@ handlebars@4.0.11:
   optionalDependencies:
     uglify-js "^2.6"
 
-handlebars@4.0.12, handlebars@^4.0.1, handlebars@^4.0.3:
+handlebars@4.0.12:
   version "4.0.12"
   resolved "https://registry.yarnpkg.com/handlebars/-/handlebars-4.0.12.tgz#2c15c8a96d46da5e266700518ba8cb8d919d5bc5"
   integrity sha512-RhmTekP+FZL+XNhwS1Wf+bTTZpdLougwt5pcgA1tuz6Jcx0fpH/7z0qd71RKnZHBCxIRBHfBOnio4gViPemNzA==
@@ -10923,14 +10923,15 @@ handlebars@4.0.12, handlebars@^4.0.1, handlebars@^4.0.3:
   optionalDependencies:
     uglify-js "^3.1.4"
 
-handlebars@4.5.3:
-  version "4.5.3"
-  resolved "https://registry.yarnpkg.com/handlebars/-/handlebars-4.5.3.tgz#5cf75bd8714f7605713511a56be7c349becb0482"
-  integrity sha512-3yPecJoJHK/4c6aZhSvxOyG4vJKDshV36VHp0iVCDVh7o9w2vwi3NSnL2MMPj3YdduqaBcu7cGbggJQM0br9xA==
+handlebars@4.7.6, handlebars@^4.0.1, handlebars@^4.0.3:
+  version "4.7.6"
+  resolved "https://registry.yarnpkg.com/handlebars/-/handlebars-4.7.6.tgz#d4c05c1baf90e9945f77aa68a7a219aa4a7df74e"
+  integrity sha512-1f2BACcBfiwAfStCKZNrUCgqNZkGsAT7UM3kkYtXuLo0KnaVfjKOyf7PRzB6++aK9STyT1Pd2ZCPe3EGOXleXA==
   dependencies:
+    minimist "^1.2.5"
     neo-async "^2.6.0"
-    optimist "^0.6.1"
     source-map "^0.6.1"
+    wordwrap "^1.0.0"
   optionalDependencies:
     uglify-js "^3.1.4"