Bump to mono:2019-02

.gitmodules

@@ -8,7 +8,7 @@
 [submodule "external/mono"]
     path = external/mono
     url = ../../mono/mono.git
-    branch = 2018-08
+    branch = 2019-02
 [submodule "external/opentk"]
     path = external/opentk
     url = ../../mono/opentk.git

Make.config

@@ -47,13 +47,13 @@ XCODE94_URL=http://xamarin-storage/bot-provisioning/xcodes/Xcode_9.4.xip
 XCODE94_DEVELOPER_ROOT=/Applications/Xcode94.app/Contents/Developer
 
 # Minimum Mono version for building XI/XM
-MIN_MONO_VERSION=5.18.0.185
-MAX_MONO_VERSION=5.18.99
-MIN_MONO_URL=https://xamjenkinsartifact.azureedge.net/build-package-osx-mono/2018-08/149/ea740d2bc8d58d9c0ee44ef0ba15ccddeafbe227/MonoFramework-MDK-5.18.0.185.macos10.xamarin.universal.pkg
+MIN_MONO_VERSION=6.0.0.6
+MAX_MONO_VERSION=6.0.99
+MIN_MONO_URL=https://xamjenkinsartifact.azureedge.net/build-package-osx-mono/2019-02/7/12cadb2b21da7f1ad8f5999fd2c5ec8a127c5795/MonoFramework-MDK-6.0.0.6.macos10.xamarin.universal.pkg
 
 # Minimum Mono version for Xamarin.Mac apps using the system mono
-MIN_XM_MONO_VERSION=5.18.0.185
-MIN_XM_MONO_URL=https://xamjenkinsartifact.azureedge.net/build-package-osx-mono/2018-08/149/ea740d2bc8d58d9c0ee44ef0ba15ccddeafbe227/MonoFramework-MDK-5.18.0.185.macos10.xamarin.universal.pkg
+MIN_XM_MONO_VERSION=6.0.0.6
+MIN_XM_MONO_URL=https://xamjenkinsartifact.azureedge.net/build-package-osx-mono/2019-02/7/12cadb2b21da7f1ad8f5999fd2c5ec8a127c5795/MonoFramework-MDK-6.0.0.6.macos10.xamarin.universal.pkg
 
 # Minimum Visual Studio version
 MIN_VISUAL_STUDIO_URL=https://bosstoragemirror.azureedge.net/vsmac/7a/7aff2dc1f28d711d11d63d79b2a4c49cda217189/VisualStudioForMac-Preview-7.7.0.1470.dmg

external/mono

@@ -1 +1 @@
-Subproject commit 2359cba40e94accdcf5ce526572bce834d53f3aa
+Subproject commit 6fe4c149ee6b49922a8bcbe80addb685e5ab75f7