Update Travis build matrix

.travis.yml

@@ -1,29 +1,17 @@
 language: rust
 
-matrix:
-  include:
-    #- env: TARGET=x86_64-unknown-linux-gnu
-    #  if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
-
-    #- env: TARGET=riscv32imac-unknown-none-elf
-    #  if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
-
-    #- env: TARGET=x86_64-unknown-linux-gnu
-    #  rust: beta
-    #  if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
+env:
+  - TARGET=x86_64-unknown-linux-gnu
+  - TARGET=riscv32imac-unknown-none-elf
 
-    #- env: TARGET=riscv32imac-unknown-none-elf
-    #  rust: beta
-    #  if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
-
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: nightly
-      if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
+rust:
+  - nightly
+  - stable
 
-    - env: TARGET=riscv32imac-unknown-none-elf
-      rust: nightly
-      if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
+if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
 
+matrix:
+  include:
     - env: TARGET=riscv64imac-unknown-none-elf
       rust: nightly
       if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
@@ -32,13 +20,6 @@ matrix:
       rust: nightly
       if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
 
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: stable
-      if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
-
-    - env: TARGET=riscv32imac-unknown-none-elf
-      rust: stable
-      if: (branch = staging OR branch = trying OR branch = master) OR (type = pull_request AND branch = master)
 
 before_install: set -e