Move to the mattermost/go-i18n fork (#10669)

This change is being made to address an issue where the go-i18n
translation library would result in partial-translations when a
given language dictionary was missing a given plural keyword. The
improvement made here leads the translation library to try an
'other' keyword lookup if the first plural keyword fails to have
a value.

This change was not accepted upstream due to concern regarding
changing the behavior, so we are using a fork at this time to
address the issue.

go.sum

@@ -206,6 +206,8 @@ github.com/mailru/easyjson v0.0.0-20180730094502-03f2033d19d5/go.mod h1:C1wdFJiN
 github.com/mailru/easyjson v0.0.0-20190312143242-1de009706dbe h1:W/GaMY0y69G4cFlmsC6B9sbuo2fP8OFP1ABjt4kPz+w=
 github.com/mailru/easyjson v0.0.0-20190312143242-1de009706dbe/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
 github.com/marstr/guid v0.0.0-20170427235115-8bdf7d1a087c/go.mod h1:74gB1z2wpxxInTG6yaqA7KrtM0NZ+RbrcqDvYHefzho=
+github.com/mattermost/go-i18n v1.1.2 h1:iyIztdnCePILpzW1nsZSLQtqhtI6M5E3OS6IkFv/BMw=
+github.com/mattermost/go-i18n v1.1.2/go.mod h1:RyS7FDNQlzF1PsjbJWHRI35exqaKGSO9qD4iv8QjE34=
 github.com/mattermost/gorp v2.0.1-0.20190301154413-3b31e9a39d05+incompatible h1:FN4zK2wNig7MVVsOsGEZ+LeIq0gUcudn3LEGgbodMq8=
 github.com/mattermost/gorp v2.0.1-0.20190301154413-3b31e9a39d05+incompatible/go.mod h1:0kX1qa3DOpaPJyOdMLeo7TcBN0QmUszj9a/VygOhDe0=
 github.com/mattermost/rsc v0.0.0-20160330161541-bbaefb05eaa0 h1:G9tL6JXRBMzjuD1kkBtcnd42kUiT6QDwxfFYu7adM6o=
@@ -240,8 +242,6 @@ github.com/muesli/smartcrop v0.2.1-0.20181030220600-548bbf0c0965/go.mod h1:i2fCI
 github.com/mwitkow/go-conntrack v0.0.0-20161129095857-cc309e4a2223/go.mod h1:qRWi+5nqEBWmkhHvq77mSJWrCKwh8bxhgT7d/eI7P4U=
 github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646 h1:zYyBkD/k9seD2A7fsi6Oo2LfFZAehjjQMERAvZLEDnQ=
 github.com/nfnt/resize v0.0.0-20180221191011-83c6a9932646/go.mod h1:jpp1/29i3P1S/RLdc7JQKbRpFeM1dOBd8T9ki5s+AY8=
-github.com/nicksnyder/go-i18n v1.10.0 h1:5AzlPKvXBH4qBzmZ09Ua9Gipyruv6uApMcrNZdo96+Q=
-github.com/nicksnyder/go-i18n v1.10.0/go.mod h1:HrK7VCrbOvQoUAQ7Vpy7i87N7JZZZ7R2xBGjv0j365Q=
 github.com/oklog/run v1.0.0 h1:Ru7dDtJNOyC66gQ5dQmaCa0qIsAUFY3sFpK1Xk8igrw=
 github.com/oklog/run v1.0.0/go.mod h1:dlhp/R75TPv97u0XWUtDeV/lRKWPKSdTuV0TZvrmrQA=
 github.com/olekukonko/tablewriter v0.0.1 h1:b3iUnf1v+ppJiOfNX4yxxqfWKMQPZR5yoh8urCTFX88=
@@ -264,6 +264,8 @@ github.com/pborman/uuid v1.2.0 h1:J7Q5mO4ysT1dv8hyrUGHb9+ooztCXu1D8MY8DZYsu3g=
 github.com/pborman/uuid v1.2.0/go.mod h1:X/NO0urCmaxf9VXbdlT7C2Yzkj2IKimNn4k+gtPdI/k=
 github.com/pelletier/go-toml v1.2.0 h1:T5zMGML61Wp+FlcbWjRDT7yAxhJNAiPPLOFECq181zc=
 github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
+github.com/pelletier/go-toml v1.3.0 h1:e5+lF2E4Y2WCIxBefVowBuB0iHrUH4HZ8q+6mGF7fJc=
+github.com/pelletier/go-toml v1.3.0/go.mod h1:PN7xzY2wHTK0K9p34ErDQMlFxa51Fk0OUruD3k1mMwo=
 github.com/peterbourgon/diskv v0.0.0-20171120014656-2973218375c3/go.mod h1:uqqh8zWWbv1HBMNONnaR/tNboyR3/BZd58JJSHlUSCU=
 github.com/pierrec/lz4 v2.0.5+incompatible/go.mod h1:pdkljMzZIN41W+lC3N2tnIh5sFi+IEE17M5jbnwPHcY=
 github.com/pkg/errors v0.8.0/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=