Update minimum Linux kernel version 2.6.22 (#814)

Bump the minimum version after crystal-lang/crystal#15335

docs/syntax_and_semantics/platform_support.md

@@ -21,8 +21,8 @@ and drop into *Tier 2*.
 | ------ | ----------- | ------------------ | ------- |
 | `aarch64-darwin` | Aarch64 macOS<br> (Apple Silicon) | 11+ *(testing only on 14)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds |
 | `x86_64-darwin` | x64 macOS<br> (Intel) | 11+<br> *(testing only on 13; expected to work on 10.7+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds |
-| `x86_64-linux-gnu` | x64 Linux | kernel 4.14+, GNU libc 2.26+<br> *(expected to work on kernel 2.6.18+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds |
-| `x86_64-linux-musl` | x64 Linux | kernel 4.14+, MUSL libc 1.2+<br> *(expected to work on kernel 2.6.18+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds |
+| `x86_64-linux-gnu` | x64 Linux | kernel 4.14+, GNU libc 2.26+<br> *(expected to work on kernel 2.6.22+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds |
+| `x86_64-linux-musl` | x64 Linux | kernel 4.14+, MUSL libc 1.2+<br> *(expected to work on kernel 2.6.22+)* | :material-checkbox-marked-circle: tests<br> :material-checkbox-marked-circle: builds |
 
 ***
 
@@ -38,8 +38,8 @@ Details are described in the *Comment* column.
 | `aarch64-linux-gnu` | Aarch64 Linux | GNU libc 2.26+ | :material-checkbox-marked-circle: tests<br> :material-selection-ellipse: builds |
 | `aarch64-linux-musl` | Aarch64 Linux | MUSL libc 1.2+ | :material-checkbox-marked-circle: tests<br> :material-selection-ellipse: builds |
 | `arm-linux-gnueabihf` | Aarch32 Linux<br> (hardfloat) | GNU libc 2.26+ | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |
-| `i386-linux-gnu` | x86 Linux | kernel 4.14+, GNU libc 2.26+<br> *(expected to work on kernel 2.6.18+)* | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |
-| `i386-linux-musl` | x86 Linux | kernel 4.14+, MUSL libc 1.2+<br> *(expected to work on kernel 2.6.18+)* | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |
+| `i386-linux-gnu` | x86 Linux | kernel 4.14+, GNU libc 2.26+<br> *(expected to work on kernel 2.6.22+)* | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |
+| `i386-linux-musl` | x86 Linux | kernel 4.14+, MUSL libc 1.2+<br> *(expected to work on kernel 2.6.22+)* | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |
 | `x86_64-openbsd` | x64 OpenBSD | 6+ | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |
 | `x86_64-freebsd` | x64 FreeBSD | 12+ | :material-selection-ellipse: tests<br> :material-selection-ellipse: builds |